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Vesisanasto

A

• Acid sulphate soils

  Acid sulphate soils are layers of soil with a high sulphur and iron content found on low-lying coasts, especially along the Gulf of Bothnia. Iron and other metals may dissolve into water from acidic sulphate soils if the groundwater surface fluctuates or other changes occur in the hydrological conditions. This causes acidification of the groundwater. If, for example, a long dry period is followed by heavy rain that leaches sulphate soils, even surface waters can become temporarily acidified.

• Acidification

  Acidification means that the ability of a lake, forest land or other habitat to neutralise acids is reduced. As a result of acidification, the pH of lake water, ditch water or soil water goes down; in other words, the water becomes more acidic. This changes the living conditions of organisms to the extent that some species may disappear.

• Acidity

  Acidity is one of the quality elements of water. Acidity is expressed on a pH scale where the value of neutral water is 7. Fresh waters in Finland are usually slightly acidic (pH 6.5 to 6.8). Seawater, on the other hand, is slightly alkaline (pH approx. 8). Groundwaters in Finland are usually slightly acidic (pH 5.9 to 6.9).

• Algae bloom

  Algae bloom refers to rapid proliferation of microscopic plankton, usually blue-green algae, in the surface layer of water. In reality the algae do not produce flowers, and the dyeing or thickening of the water is caused by the algae themselves. Such mass occurrence can emerge quickly when the weather conditions are favourable.

• Alien plant species

  An alien plant species is a plant that, rather than having spread into an area naturally, has been introduced by humans, either intentionally or unintentionally. Alien plants may compete for space with native species.

• Alien species

  An alien species is an organism that, rather than having spread into an area naturally, has been introduced by humans, either intentionally or unintentionally. Alien species may compete or hybridise with native species, prey on them or spread diseases.

• Antifouling paint

  Antifouling paints are paints applied to the bottoms of boats to prevent hard shell aquatic organisms, including barnacles, from attaching to them. Antifouling paints are harmful to the aquatic environment, and their use in inland waters is prohibited.

• Aquaculture

  Aquaculture refers to the managed farming of fish, crayfish and other aquatic organisms in an inland water body, the sea or an artificial basin.

• Aquascope

  An aquascope is a simple tool for observing the underwater world. The cone-shaped aquascope has a transparent bottom and an opening at the top for looking through. The bottom part is pushed into the water, which prevents the refraction of light at the water surface from distorting the view. You can purchase ready-made aquascopes, but you can also make one yourself, for example from a plastic bucket and a sheet of plexiglass.

• Aquifer

  An aquifer is a layer in the Earth’s crust that stores and conducts water in such quantities that a well can be made in that area.

• Arsenic

  Arsenic is a semi-metal that occurs naturally in the Earth’s crust. The most common arsenic mineral in Finland is arsenic sulfide. Arsenic may leach from bedrock into groundwater, especially in fracture zones where arsenic sulfide comes into contact with groundwater. In some drilled wells, arsenic has been found in concentrations that are harmful to human health.

• Arterial drainage

  Arterial drainage includes excavation and clearing of main ditches, the building of small embankments and improving the water capacity of brooks carried out for drainage purposes. Arterial drainage creates the prerequisites for field drainage, which includes smaller-scale and subsurface drainage.

• Artificial lake

  An artificial lake, or a man-made lake, is a lake built or dammed by humans. Artificial lakes have been built for many purposes. Many of them operate as reservoirs for hydropower plants, while others are used for flood protection, water services or recreation.

• Artificially recharged groundwater

  Artificially recharged groundwater is groundwater whose volume has been increased by infiltrating lake or river water into the ground. In Finland, nearly 30 water utilities use groundwater that has been artificially recharged.

• Atmospheric deposition

  Atmospheric deposition refers to materials that are deposited from the air into water or on the ground. The deposition can originate from nearby emissions or from distant emission sources even thousands of kilometres away. The latter is referred to as long-range transboundary air pollution.

• Atmospheric pressure

  Atmospheric pressure refers to the pressure of the atmosphere against the Earth’s surface. Normal atmospheric pressure is 1,013 hectopascals (or millibars, which is an obsolete unit). The atmospheric pressure varies, and winds are created by regional pressure differences.

B

• Backwater height

  Backwater height is the level to which water can rise in the sewer network if, for example, a sewer is blocked.

• Barrier to migration

  A barrier to migration refers to a dam or other structure that prevents fish and other aquatic organisms from spreading or migrating in the river system between their spawning and living areas. If a dam cannot be removed, it can be bypassed using a fish pass.

• Bedrock groundwater

  Bedrock groundwater is groundwater that is filtered directly from precipitation or the ground into cracks in the rock. Drilled wells can be used to obtain bedrock groundwater.

• Benefits of drainage

  The benefits of drainage refer to an increase in the value of the purpose for which the land is used, or can mainly be used, which can be achieved by means of drainage.

• Benthic fauna

  Benthic fauna are invertebrates which, at least at some stage of their life cycle, mainly live on the surfaces of the bottom or on stones, plants or within the bottom sediment. Benthic animal species are, among other things, influenced by the quality of the bottom and the oxygen content in the water and sediment.

• Bifurcation

  In hydrology, bifurcation refers to a flow that divides into two branches that no longer join together. Bifurcations can be divided into two main types: lake and river bifurcations. In river bifurcation, a river is divided into two downstream channels. In lake bifurcation, the waters of a lake are discharged in different directions along two outlets.

• Biocoenosis

  A biocoenosis is a community that consists of populations of species living in the same area and their interactions. A biocoenosis includes all organisms found in the area. Environmental changes often also change the composition of the biocoenosis.

• Biofiltration area

  Biofiltration areas, swales and green roofs covered with vegetation are stormwater treatment systems into which stormwaters are directed and in which they are absorbed and filtered before they are led further. Swales are open depressions covered with vegetation which can be constructed along a road, for example.

• Biological oxygen demand

  Biological oxygen demand (BOD) refers to the amount of oxygen consumed by organic matter in water or wastewater in a biological reaction. The majority of the biological oxygen demand in domestic wastewater is caused by toilet sewage.

• Biomanipulation

  Biomanipulation refers to measures targeted at supporting the healthy functioning of the food web of a lake affected by eutrophication. Biomanipulation aims at reducing the amount of nutrients and mitigating eutrophication by removal of planktivorous and benthic feeding fish. Biomanipulation may include intensive fishing to manage cyprinid fish populations or stocking the lake with predatory fish.

• Biomass

  Biomass is the total volume of living organisms (in wet weight, dry weight or energy) in a certain environment at a given moment.

• Biotope

  A biotope is a water or land area with specific environmental conditions and characteristic plant and animal communities.

• Black ice

  Black ice, or clear ice, is hard ice formed when water freezes directly, without being mixed with snow. The bearing strength of ice is always expressed for black ice.

• Blackwater

  Blackwater refers to sewage from a flushable toilet. It contains urine and faeces, which makes it more demanding to treat than water used for washing.

• Blue water footprint

  The blue water footprint refers to the volume of water obtained from natural water reserves, in other words rivers, lakes and groundwater reserves, that is consumed by a person, a state or the manufacture of a specific product, for example. In this calculation, both direct and indirect water consumption are taken into account.

• Blue-green algae

  Blue-green algae (cyanobacteria) are photosynthetic bacteria that occur naturally in all bodies of surface water. Many species of blue-green algae are able to use nitrogen dissolved in water from the atmosphere. This enables them to proliferate even when the lack of nitrogen limits the growth of other algae. Some blue-green algae are toxic.

• Blue-green algae toxins

  Blue-green algae toxins are compounds produced by blue-green algae that are harmful to other organisms. Only some of the blue-green algae produce toxic compounds, and some strains of the same species can be toxic, while others are not. Blue-green algae toxins in water cannot be eliminated by boiling.

• Brook

  The Water Act defines a brook as a water body with flowing water, smaller than a river. The catchment of a brook is smaller than that of a river, in other words less than one hundred square kilometres. Unlike in a streamlet, water in a brook flows continuously.

• Buffer strip

  A buffer strip, or buffer zone, is a strip between a field or cut forest area and a water body that is not cultivated or managed and that has permanent plant or tree cover. The purpose of the buffer strip is to reduce erosion and the transport of nutrients and pesticides into waters. The buffer strip also increases biodiversity and species richness in both water bodies and buffer areas.

• Buffer zone

  A buffer zone is a strip between a field or cut forest area and a water body that is not cultivated or managed and that has permanent plant or tree cover. The purpose of the buffer zone is to reduce erosion and the transport of nutrients and pesticides into waters.

C

• Calculation model

  Calculation models are tools for assessing water quality, emissions or hydrological conditions when they cannot be measured directly, or anticipating them is necessary. Calculation models can be highly complex as they must account for a large number of factors.

• Capillary action

  Capillary action regulates the flow of a liquid, such as water, in a very thin tube or pore structure. Capillary action makes it possible for water to flow upwards in compacted soil. This is explained by the fact the forces between molecules are greater between a liquid and a solid material than within a liquid.

• Carbon balance

  Carbon balance is the relationship between carbon sequestration and carbon emissions over a certain period of time. A positive carbon balance means that more carbon has been sequestered than released into the atmosphere.

• Carbon dioxide

  Carbon dioxide is a gaseous compound consisting of carbon and oxygen. Its chemical formula is CO₂. Carbon dioxide occurs naturally in the Earth’s atmosphere at low concentrations, but the carbon dioxide emissions produced by humans have increased its concentration, resulting in global warming. Carbon dioxide that dissolves from the atmosphere into the oceans causes acidification of sea water.

• Carbon footprint

  Carbon footprint refers to greenhouse gas emissions caused by a product, service or, for example, a municipality or a private citizen. When calculating the carbon footprint, all direct and indirect emissions must be taken into account. Indirect emissions include emissions from the production and transport of raw materials used in products.

• Carbon neutral

  Carbon neutral refers to a situation where greenhouse gas emissions and carbon sinks are in balance. Finland has set the target at being carbon neutral in 2035. This would mean that the volume of carbon sequestered from the atmosphere in forests and other carbon sinks would equal the greenhouse gas emissions produced by Finland.

• Carbon sequestration

  Carbon sequestration refers to the long-term sequestration and storage of atmospheric carbon (carbon dioxide) in forests, the soil or seas. Carbon sequestration may also mean the capture of carbon dioxide from flue gases or removing carbon dioxide from the atmosphere.

• Carbon sink

  A carbon sink is an ecosystem or part of an ecosystem capable of sequestering or binding carbon dioxide from the atmosphere and storing carbon for a long period of time. Typical carbon sinks include forests, oceans and mires.

• Catchment

  The catchment, or drainage basin, of a water body is the land area where topographic features direct any rainfall into the system in question.

• Catchment restoration

  Catchment restoration is a major part of a project to restore a water body. Its objective is to reduce the load entering the aquatic system from the catchment in order to achieve long-term improvements in the water body. Catchment restoration measures may include building wetlands and channels with floodplains as well as peatland restoration.

• Cavity frost

  Cavity frost is characteristic for soil with a friable structure, such as a ploughed field. It is formed when water freezes on cavity walls. Cavity frost crystals are rod-like in structure.

• Chemical oxygen demand

  Chemical oxygen demand (COD) refers to the amount of oxygen consumed by substances in water in a chemical reaction. For example, humus and organic substances in wastewater increase chemical oxygen demand.

• Chemical status

  The assessment of the chemical status of surface waters is based on whether or not the water fulfils the environmental quality standards for certain hazardous and harmful substances. The assessment covers 53 substances or groups of substances. If the limit value of even one of these substances is exceeded, the chemical status of the water will not receive the grade ‘good’.

• Chemicalisation

  Chemicalisation refers to the increasing occurrence of artificial chemicals in nature and living environments. Chemicalisation is a cause for concern as huge numbers of different chemicals are in use whose long-term environmental and health impacts are not known. For instance, chemicalisation is considered a possible reason for the deterioration in Finnish men’s sperm quality.

• Chlorophyll a

  Chlorophyll a is used as an indicator of phytoplankton biomass and of the general eutrophication status of a water body. The chlorophyll a concentration varies during the year. The greatest values are seen during maximum algal growth in spring and blue-green algae occurrences in summer.

• Classification of groundwater areas

  Groundwater areas are classified on the basis of their suitability for water supply and protection needs: Class 1 comprises groundwater areas that are important for water supply and where the volume used, or intended to be used, is more than 10 m³/day or meeting the needs of more than 50 people; class 2 comprises groundwater areas that, due to their characteristics, are suitable for similar use. Class E includes groundwater areas producing groundwater on which protected surface water or terrestrial ecosystems are directly dependent.

• Climate change

  Climate change refers to long-term change in the global climate system, as a result of which the general nature of weather conditions changes. Climate change can result from natural causes, including major volcanic eruptions. In today’s context, climate change mainly refers to global warming caused by humans and its consequences.

• Climate model

  A climate model is a simplified description of the Earth’s climate system or some part of it based on mathematical equations. These equations are derived from the laws of physics. With different assumptions, climate models can be used to assess climate change in the past and predict it in the future.

• Climate Panel

  The term Climate Panel may refer to either the Intergovernmental Panel on Climate Change (IPCC) or the Finnish Climate Change Panel. Both are scientific and independent expert bodies. The task of the Finnish Climate Change Panel is to plan Finland’s climate policy and support decision-making concerning it.

• Climate scenario

  Climate scenarios are different visions of how the climate will develop in the future. The scenarios are based on the best available estimates (often produced by climate models) of how the climate will change with various input assumptions, such as different greenhouse gas emission volumes.

• Coastal flood

  A coastal flood, or a sea water flood, is caused by an exceptionally high sea level and results in the flooding of land areas. Five coastal flood risk areas have been identified in Finland. Climate change can increase the risk of coastal flooding.

• Collecting ditch

  Collecting ditches are ditches into which waters from field drains or subsurface drains are led. Collecting ditches can be equipped with water protection structures, for example in connection with ditch maintenance.

• Colour of water

  The colour of water varies in natural water bodies depending on the types and concentrations of coloured substances in the water. The most common substances staining water in Finland are humus and iron. In limestone areas, water often looks turquoise. The turquoise colour results from limestone sand and dust mixed in the water.

• Combined sewer

  A combined sewer is a sewer that carries both stormwater (rainwater) and sewage. Combined sewers are no longer built, but they may still exist in old residential areas. Water from combined sewers is led to a sewage treatment plant.

• Cyanobacteria

  Cyanobacteria (blue-green algae) are photosynthetic bacteria that occur naturally in all bodies of surface water. Many species of blue-green algae are able to use nitrogen dissolved in water from the atmosphere. This enables them to proliferate even when the lack of nitrogen limits the growth of other algae. Some blue-green algae are toxic.

D

• Dam

  A dam is a structure, such as a wall or embankment, whose purpose is to regulate the flow or height of water or to prevent the spread of water or other liquids impounded by the dam. Dam structures can be earth banks or concrete structures, and they can also be entirely submerged.

• Dam Safety Act

  The purpose of the Dam Safety Act, revised in 2009 (DSA 494/2009), is to ensure safety in the construction, maintenance and operation of a dam and reduce the hazard that may be caused by a dam. The act contains provisions on the obligations of the dam owner as well as the supervision of dams and the duties of different authorities.

• Detention basin

  A detention basin is a basin for detaining stormwaters or other waters.

• Diatom

  Diatoms are single-cell algae that live separately or as colonies. Their name is derived from their Latin genus name Diatoma. Diatoms are found both on bottom surfaces and floating in the water. Surface-dwelling diatoms may form a slimy layer and, for example, cause sliming of fishing nets. Planktonic diatoms often are beautifully symmetric when seen under the microscope.

• Diffuse pollution

  Diffuse pollution, or non-point source pollution, refers to the pollution loading of a water body that consists of several small emission sources which cannot be accurately determined. Diffuse pollution includes solids and nutrient load from fields, livestock farming and forestry as well as wastewater from sparsely populated areas.

• Dinoflagellate

  Dinoflagellates are relatively large single-cell algae that belong to phytoplankton. They usually have a hard shell and two flagella that enable them to move in water. Some dinoflagellates may produce neurotoxins. Mass occurrences of dinoflagellates have been known to cause fish kills in the sea.

• Discharge

  Discharge, or flow rate, refers to the volume of water that goes through a channel cross-section or some river basin in a certain time unit. Discharge can be measured with a flow meter or, in smaller water bodies, with a weir. In stable channels, discharge values can be obtained from water level observations using a so-called rating curve.

• Discharge well

  A discharge well is a well in a wastewater or stormwater system from which water is discharged into a water body or to some other destination. A discharge well may also refer to a component at the end of a pressurised sewer system from which the wastewater is led into a collector sewer or some other sewage pipeline.

• Disinfection

  Disinfection is a treatment phase in which bacteria and other microbes are destroyed. Disinfection is an important part of tap water production. Ozone, ultra-violate radiation or chlorine can be used for this purpose.

• Ditch break

  A ditch break is a ditch section that has not been excavated in drainage or ditch network maintenance. Ditch breaks reduce water flow velocity and may thus retain solids that drainage activities have released. They may also reduce erosion by diminishing flow velocity.

• Ditch network maintenance

  Ditch network maintenance refers to the cleaning of old ditches and possible excavation of additional ones. The purpose of ditch network maintenance is sufficient water table depth for forest growth.

• Domestic water treatment plant

  A domestic water treatment plant is a small plant intended for treating wastewater in sparsely populated areas. It usually consists of one or more tanks, a control centre and a discharge arrangement. A domestic water treatment plant operates on the same principle as municipal wastewater treatment plants.

• Drainage

  In the Water Act, drainage refers to both digging a new ditch and maintaining and improving an existing drainage channel, i.e. enlarging, straightening out or cleaning a ditch, streamlet or brook.

• Drainage association

  A drainage association is established by a decision issued in drainage proceedings for drainage or maintenance. The members of the drainage association are those who benefit from the drainage. The rules of the drainage association are confirmed by the Regional State Administrative Agency or the executing official handling the drainage matter. The drainage association may be dissolved by a decision made in drainage proceedings. Before the drainage association is dissolved, the ditches must be returned to a natural-like state.

• Drainage notification

  The purpose of a drainage notification is to enable the supervisory authorities to assess whether a water permit or drainage proceedings are needed for the project – or under what conditions and restrictions the project can be implemented without a permit or drainage proceedings. The notification must be submitted to the ELY Centre no later than 60 days before undertaking drainage operations.

• Drainage plan

  A drainage plan must be drawn up if either a permit issued pursuant to the Water Act or drainage proceedings is required for the project. The plan contains information on the project and its implementation and on drainage depth, as well as a plan for water protection, an account of the benefit to be gained from the project, and an assessment of the impacts of the project.

• Drainage proceedings

  Drainage proceedings are a procedure in which a drainage plan and the prerequisites for its implementation are examined, a cost estimate is prepared, and a decision is made on the allocation of costs between different parties. Drainage proceedings are carried out for extensive drainage projects involving several properties.

• Dredging

  Dredging refers to deepening a water area by excavating or pumping sludge and sediments from the bottom. Dredging is used as one of the management measures of shallow shores and lakes at risk of becoming overgrown. Dredging can also be detrimental; it can increase water turbidity and release nutrients and harmful substances from the sediment and destroy fish spawning grounds.

• Drift ice

  Drift ice is ice that floats freely in the sea. It is not attached to the shoreline or skerries like fast ice. Drift ice may drift with the wind or currents and pile up to form pack ice.

• Drilled well

  A drilled well is a borehole drilled into the bedrock from which groundwater is extracted. The capacity of a drilled well is not very high, as the groundwater flows slowly through cracks in the rock. However, it usually yields quite enough water for an individual household’s needs.

• Drinking Water Directive

  The revised EU Drinking Water Directive entered into force in January 2021. Its objective is to protect citizens and the environment from the harmful effects of contaminated drinking water and to improve the availability of drinking water. Among other things, the directive contains provisions on the quality, control and risk management of drinking water and provision of information on water quality.

• Drizzle

  Drizzle occurs when water droplets in the air are dense and smaller than usual (0.2–0.5 mm), allowing them to be carried along with the movements of air flows. If drizzle freezes into a thin layer on the ground surface in winter, this is referred to as freezing drizzle.

• Drought

  Drought refers to a prolonged period of time during which an area has less water than average. A drought can be caused by lack of precipitation, groundwater, surface water or all of these.

• Drought risk

  The elements of drought risk are a drought hazard, sites and activities exposed to drought, and their vulnerabilities.

• Drought risk management

  Drought risk management refers to a set of measures aimed at assessing and reducing drought risks and preventing or reducing harms caused by a drought.

• Drought risk management plan

  A drought risk management plan is a plan drawn up for an area stating how damage caused by a drought can be prevented or mitigated. Drought risk management plans are currently prepared on a voluntary basis.

• Dry season

  A dry season can be determined on the basis of meteorological or hydrological criteria or by considering exposed sectors, including agriculture and water supply. The duration of a dry season may be from a month to several years.

• Dug well

  A dug well is the most common well type. It is dug into the ground and supported by concrete well rings, which are carefully sealed. The well bottom is covered with a layer of filter gravel that is 20 to 50 centimetres in thickness.

E

• Ecological corridor

  An ecological corridor is a narrow zone, such as a river or brook with no barriers, that connects larger separate habitat patches, including lakes. An ecological corridor makes it possible for organisms to move from one patch to another.

• Ecological status

  The ecological status of surface waters is assessed using a five-step scale. The assessment is primarily based on biological quality elements, such as phytoplankton, aquatic flora, fish and benthic fauna. In addition, factors describing water quality and hydromorphology are taken into account. The reference point is a natural state that has not been influenced by human action.

• Ecosystem

  An ecosystem is a functional community of interacting organisms and their physical environment with relatively uniform ecological conditions. A lake, for example, can comprise a single ecosystem. It can also be divided into pelegial (open water), profundal (bottom) and littoral (shore) ecosystems.

• Ecosystem service

  Ecosystem services are tangible and intangible benefits produced by ecosystems for humans. Ecosystem services include provisioning services (for example, food and materials), supporting services (nutrient recycling), regulating services (climate regulation) and cultural services (recreation and inspiration).

• Electrical conductivity

  Electrical conductivity is one of the parameters of water quality. It indicates the volume of minerals (salts) dissolved in water. Electrical conductivity is usually low in Finnish inland water bodies as the quantities of calcium carbonate or other salts are small. Loading from the catchment may increase electrical conductivity in a water body.

• Elevation model

  An elevation model is a numerical representation of the Earth’s surface that contains actual height points representing the topography. Typically, the elevation model is stored in a data system as a regular grid. The most accurate elevation model available nationally in Finland is KM2 (with 2-metre grids) based on laser scanning produced by the National Land Survey of Finland.

• Emergency high water level

  Emergency high water level, or emergency water level, is a concept related to dam safety. It is determined on the basis of the core of an embankment dam or the lowest point of a concrete dam. If this level varies, the emergency level is determined by its lowest point. If the water level rises above the emergency level, it may result in changes in dam structures.

• Energy efficiency

  Energy efficiency means that the amount of energy consumed, such as electricity or fuel, is small in proportion to the work, product or service obtained. Energy efficiency helps to reduce greenhouse gas emissions cost-effectively.

• Enhanced nitrogen removal

  Enhanced nitrogen removal refers to complementing standard wastewater treatment with special arrangements for removing nitrogen. Enhanced nitrogen removal is used especially at wastewater treatment plants that discharge into nitrogen-sensitive sea areas.

• Environmental flow

  Environmental flow is the flow that the river ecosystem needs to thrive. When the flow in a regulated river is adjusted to the environmental flow, a good ecological status can be achieved. The quantity, quality and timing of the environmental flow is determined individually for each river. The term ecological flow is used in natural rivers.

• Environmental permit

  An environmental permit is needed for activities involving a risk of environmental pollution and it is issued by the environmental permit authority. In certain cases, where the activity only causes a minor impact on the environment, it is sufficient for the operator to submit a written notification of it to the authority.

• Erosion control

  The purpose of erosion control is to prevent soil erosion or, for example, to stop soil and nutrients leached from fields being carried to the water body. Plants that bind soil and nutrients, embankments and stream deflectors, or special geotextiles and willow matting can be used for erosion control.

• Eutrophication

  Eutrophication refers to the proliferation of algae and other organisms performing photosynthesis due to receiving more nutrients. This results in a wide range of changes: turbidity of water, mass occurrences of algae and excessive growth of aquatic plants, increased abundance of cyprinid fish species, overgrowth of plants on the shorelines, and oxygen depletion that may affect the deep water areas.

• Evaporation

  Evaporation is a meteorological concept describing the magnitude of vaporization as millimetres per day, for instance.

F

• Fast ice

  Fast ice is sea ice fastened to shores and skerries. Rather than drifting with winds and currents like drift ice, it stays in place.

• Field ditch

  A field ditch is a ditch between field parcels which conveys water to a collector drain.

• Filamentous algae

  Multicellular algae which form thread-like structures are known as filamentous algae. They typically grow on stone surfaces just below the waterline, but also on other surfaces. Filamentous algae grow fast. In winter, the ice detaches filamentous algae in the waterline, but new growth starts in the spring from the basal cells left on the substrate.

• First snow cover

  A weather station official records the first snow cover when the snow depth gauge shows a snow depth of 1 cm at 8 a.m. (or 9 a.m. in summer time) for the first time in the autumn.

• Fish elevator

  A fish elevator is an automatic device that lifts migratory fish trying to swim up a river to the upstream side of a dam. The challenges include the intermittent operation of the device and attracting fish into the elevator.

• Fish lock

  A (Borland) fish lock is a solution that enables fish to get past a hydropower plant. It consists of two basins and a conduit or chamber that connects them. The effectiveness of fish locks may be undermined by their intermittent operation. The challenges also include enabling fish to find the fish lock.

• Fish pass

  A fish pass, or a fishway, allows fish to swim upstream in places where a dam or some other obstacle prevents their movements. A fish pass may be a nature-like channel made of natural stones or, for example, a technical fish pass consisting of consecutive concrete basins and small waterfalls. Water should run through the fish pass all year.

• Fisheries restoration

  The aim of fisheries restoration measures is to revive or restore natural fish populations in a water body. These measures include regulating and controlling fishing, stocking and improving the living conditions of fish (for example through selective fishing), increasing the number of juvenile production areas or removing migration barriers.

• Flada

  A flada is a brackish water basin connected to the sea by a narrow inlet but gradually separating from the sea as a result of land uplift. Over time, the flada becomes a glo lake that no longer has a connection to the sea.

• Flame retardant

  Flame retardants are chemical compounds that prevent ignition or slow down the spread of fire in a material. Flame retardants are used in textiles and plastics, among other things. Some of these substances have proven detrimental to the environment and human health, and they have now been banned. However, they continue to occur in water bodies in concentrations that exceed limit values.

• Flood

  A flood means that the ground is temporary covered with water due to rising water or sea level, or due to stormwater build-up.

• Flood area identified in a preliminary flood risk assessment

  A flood area identified in a preliminary flood risk assessment is an area that will be submerged by an unusually large flood if it were to happen. The assessment is based on hydrological data and topographical height data. A critical view should be taken of this assessment as it is a rough estimate and its input data are partly uncertain: for example, the accuracy of the height data is usually only within 1 to 2 metres. Concepts with a similar meaning include a low-lying area, a potential flood area and a rough level flood area.

• Flood channel

  A flood channel is either a natural or man-made channel in which water flows, or into which water is led, during a flood.

• Flood cover

  Flood cover refers to additional cover in insurance companies’ home or real estate insurance policies that pays compensation for damage caused by exceptional fluvial, coastal and pluvial floods to buildings or other property. Their definitions of an exceptional flood may vary, but it typically refers to a fluvial flood whose probability is once every 50 years or less. A pluvial flood is considered exceptional when precipitation reaches 30 mm per hour or 75 mm per day.

• Flood hazard map

  Flood hazard maps describe the areas covered by water and the water depth in a flood as well as the prevailing water level with a certain flood probability. At minimum, flood hazard and flood risk maps are prepared for floods whose annual probability is 2% as well as for exceptionally large floods with an annual probability of 1%.

• Flood height

  Flood height is the maximum level to which flood water rises. Flood height can be used to determine the magnitude of the largest floods observed in a water body, as well as typical floods and the smallest floods detected. Flood height can be expressed as a recurrence, such as flood height HW 1/50, or a water level, such as flood height + 73.20 m N2000.

• Flood management group

  Regional river basin and coastal flood management groups coordinate flood risk management planning in significant flood risk areas. The flood management group members represent the Regional Councils, ELY Centres, municipalities, rescue services and other authorities as well as other stakeholders. The group is appointed by the Ministry of Agriculture and Forestry in connection with the identification of significant flood risk areas.

• Flood peak

  The flood peak is the highest water level during a flood event.

• Flood plain

  A flood plain is an elongated strip of flat ground along a waterline onto which flood water can rise. The purpose of the flood plain is to prevent floods from rising into fields and to improve water management in the catchment while reducing the amount of nutrients and solids in the water body.

• Flood probability

  The annual probability and recurrence interval of a flood describe the frequency of floods. Both concepts are commonly used. The recurrence interval indicates the average time after which a flood of a certain size or greater recurs. For example, a recurrence interval of 250 years means that a flood of this magnitude is likely to occur four times in a thousand years. Consequently, its annual probability is 0.4%. Similarly, the annual probability of a flood recurring once every 100 years is 1%.

• Flood protection

  Flood protection refers to protection against floods. It may include measures aimed at preventing flooding or flood damage in a specific area. These measures may include higher shore embankments or avoiding flood-sensitive activities in flood risk areas.

• Flood protection level

  Flood protection level refers to the recurrence interval or water level of a flood against which a building or activity is protected.

• Flood relief route

  A flood relief route, or flood relief channel, is a route to which stormwaters are directed when the capacity of rainwater sewers has been exceeded.

• Flood risk

  Flood risk refers to a combination of the probability of a flood and its potentially harmful consequences for human health, safety, the environment, infrastructure, economic activity and cultural heritage.

• Flood risk area

  A flood risk area is an area exposed to a flood hazard, and where there is a potential vulnerability for flood damage. A significant flood risk area is an area identified in compliance with flood risk legislation on the basis of a preliminary assessment of flood risks.

• Flood risk grid square

  Flood risk grid squares can be used as a tool for identifying flood risk areas. The data consists of 250 m x 250 m squares. The risk class of a square, 1 to 4, is determined by the number of residents and the floor area in the square, with class 1 representing the highest risk. This method and the risk classes used are based on the risk grid square method employed by the rescue services.

• Flood risk management

  Flood risk management refers to a set of actions aimed at assessing and reducing flood risks as well as preventing or reducing damage caused by floods. Flood risk management planning includes three phases: preliminary flood risk assessment, preparation of flood maps and flood risk management planning.

• Flood risk management plan

  A flood risk management plan is a plan drawn up for a flood risk area setting out how floods and the risk of damage caused by them can be prevented or reduced. Under the law, management plans must be drawn up for significant flood risk areas.

• Flood risk map

  Flood risk maps show the number of residents, special sites, infrastructure, environmental risk sites, cultural heritage and other necessary information regarding the flood risk area.

• Flow regulation

  Flow regulation refers to regulating the flow of water, for example by means of dam gates or power plant turbines.

• Fluorine

  Fluorine is a base element naturally occurring in the Earth’s crust. It belongs to the halogen group. In the bedrock, fluorine is always found in the form of fluoride, for example as calcium fluoride (fluorite). Fluoride may dissolve in groundwater if the water remains in contact with fluorine-containing minerals for a long time. Excessive fluoride concentrations in well water mainly occur in rapakivi granite areas.

• Fog

  Fog is a general name for water droplets floating in the air. Fog is produced if the air temperature drops to the dew point or air humidity rises and reaches the saturation state. If visibility is less than one kilometre, it is called fog, and if the visibility is 1 to 10 km, it is called mist.

• Food chain restoration

  Food chain restoration is a method of restoring lakes that are affected by eutrophication. It consists of intensive fishing to manage excessively dense populations of cyprinid fish. The lake can also be stocked with predatory fish, or other measures can be taken to modify the food chain. This means that nutrients will be removed from the lake, and the internal loading of the lake will be reduced.

• Food web

  The food web consists of all the food chains in an ecosystem. At the lowest level of aquatic food webs are algae and bacteria that perform photosynthesis, followed by organisms that graze on them, including zooplankton. At the top of the food webs are apex predators, such as predatory fish, birds and seals.

• Frazil ice

  Frazil ice (slush) consists of small ice crystals formed in the supercooled water of a river stretch with a strong and turbulent flow. Supercooling happens in sub-zero temperatures when water flow prevents the formation of a protective ice cover. Ice crystals form, stick together and gradually rise to the surface, forming frazil ice floes or slush.

• Frazil ice dam

  A frazil ice dam, or hanging dam (slush jam), is created when frazil ice formed in supercooled water adheres to the bottom of a channel (anchor ice) or builds up under the ice cover, impeding the flow of water.

• Frazil ice dam

  A frazil ice dam, or slush jam (hanging dam), is formed when frazil ice formed in supercooled water adheres to the bottom of a channel (anchor ice) or builds up under the ice cover, impeding the flow of water.

• Frost depth

  Frost depth indicates the depth from the ground surface to which the ground is frozen. Frost depth measuring stations where measurements are made three times a month during the winter season are located around Finland.

• Frost heaving

  Frost heaving refers to an increase in volume or change in physical characteristics of the soil as it freezes. This happens due to the freezing of additional water flowing into the frost front. An essential factor in frost heaving is that the water (ice) content of the soil layer increases during freezing. Frost heaving also refers to soil movements caused by the melting of the frost.

G

• Glo lake

  A glo lake is a former sea bay that has lost contact with the sea. Over time, a glo lake becomes a freshwater lake.

• Grease ice

  Grease ice is a very thin and shiny layer of ice that forms on a calm water surface overnight. Grease ice is easily broken by the wind and waves.

• Green water footprint

  The green water footprint refers to the rainwater transpired by cultivated plants.

• Greenhouse effect

  The greenhouse effect is a natural phenomenon created by the Earth’s atmosphere that causes warming in the troposphere. The greenhouse effect is caused by the fact that carbon dioxide and other greenhouse gases in the atmosphere allow sunlight to reach the surface of the soil but reflect thermal radiation from the Earth back down. The intensity of the greenhouse effect depends on the amount of greenhouse gases in the atmosphere.

• Greenhouse gas

  Greenhouse gases are the gases in the atmosphere that maintain the greenhouse effect. They include carbon dioxide, methane, ozone, nitrous oxide and freons. Emissions of these gases into the atmosphere drive the greenhouse effect. Water vapour, which is naturally found in the atmosphere, is the most significant greenhouse gas with a warming effect.

• Greenhouse gas emission

  Greenhouse gas emissions are emissions into the atmosphere of gases that drive the greenhouse effect and thus cause the climate to warm. The most significant ones are carbon dioxide and methane emissions. They are mainly generated in the combustion of fossil fuels, agriculture and other land use.

• Grey water

  Grey water refers to domestic wastewater other than toilet sewage. Such activities as washing, cleaning and kitchen work produce grey water.

• Grey water footprint

  The grey water footprint refers to the volume of clean water that is consumed at production plants for rinsing and washing and for cleaning a product or purifying wastewater.

• Groundwater

  Groundwater refers to all water under the ground surface that fills open spaces in the ground and bedrock. Groundwater is produced when rain or surface water is infiltrated through soil layers or flows into cracks in the bedrock.

• Groundwater area

  The Environmental Protection Act defines a groundwater area as an area that can be delineated based on geological criteria and within which a soil formation or bedrock zone enables significant groundwater flow or intake.

• Groundwater area protection plan

  A groundwater area protection plan is an account of and guideline on how groundwater should be taken into account, for example when planning land use in an area. Protection plans are mainly drawn up for groundwater areas that are used for water supply and in which many activities that put groundwater at risk are located.

• Groundwater body

  A groundwater body is a distinct volume of groundwater within a porous and permeable soil or bedrock formation that allows a significant flow of groundwater or significant abstraction of groundwater. (Act on the Organisation of River Basin Management and the Marine Strategy)

• Groundwater deposit

  In the Water Act, a groundwater deposit refers to groundwater stored as a distinct volume of water in the saturation zone. A groundwater deposit may also be located outside the groundwater area.

• Groundwater level

  Groundwater level describes the surface level of groundwater and its fluctuations. Factors affecting the groundwater level include the size of the groundwater body, precipitation, meltwaters, evaporation and water used by vegetation. The groundwater level typically drops in the summer.

• Groundwater recharge area

  A recharge area is an area where soil layers conduct water well and where the soil enables significant water infiltration to form groundwater. Based on the recharge area, an estimated groundwater recharge volume can be calculated.

H

• Habitat

  A habitat is a living place or area of species defined by various physical and ecological factors, including the climate, topography and substrate properties. Factors defining underwater habitats include water depth, openness of the shore and the quality of the bottom.

• Halocline

  A halocline is a vertical zone in which the salinity of sea water changes rapidly over a short distance. In the Baltic Sea, the halocline typically lies at a depth of 50 to 80 metres. There is no clear salinity stratification in the Gulf of Bothnia, and the stratification in the Gulf of Finland varies in intensity.

• Helmi habitats programme

  The aim of the Ministry of the Environment’s Helmi programme 2021–2030 is to foster biodiversity in Finland and safeguard the ecosystem services provided by nature. The priorities of the programme include, among other things, restoration of mires and waterfowl habitats as well as management of small water bodies and coastal nature.

• Hidden water

  Hidden water, or virtual water, refers to the amount of water contained in products. Virtual water includes all water consumed during a product’s life cycle from raw material production until the product is treated as waste.

• High pressure

  High pressure is an area in which the atmospheric pressure is higher than in its surroundings. At the high pressure centre, the weather is usually calm, or there are slack local winds. In the northern hemisphere the wind direction is clockwise around the high-pressure area and diagonally away from the centre.

• Highest discharge

  The highest discharge (HQ), also called the high discharge or maximum discharge, is the highest discharge or flow rate of an observation period.

• Highest water level

  The highest water level (HW), also called the high water level, is the highest water level of an observation period.

• HINKU municipality

  HINKU municipalities are committed to achieving an 80% reduction in their greenhouse gas emissions by 2030 (compared to 2007 levels). Established in 2008, HINKU is a network of municipalities committed to reducing their emissions, companies offering climate-friendly products and services, and experts in the energy and climate sector.

• Holding tank

  A holding tank, also called a wastewater holding tank, is a container attached to the toilet seat in which both solid and liquid toilet waste is temporarily disposed. Holding tanks are used in boats and caravans. It is forbidden to empty a holding tank into the sea or a lake. Ports provide suction pumps for emptying holding tanks.

• Humus

  Humus is created when plant parts stored in peat or forest surface soil decay and break down. Humic substances that contain organic carbon and iron, among others, may be dissolved in water or occur as light, microscopic particles. In particular, humus is found in waters near peatlands. Humic substances give many Finnish lakes a brownish colour, as well as the Bay of Bothnia. Humus also affects water acidity.

• Hydraulic engineering

  Hydraulic engineering refers to construction in or affecting a water body. It includes dredging, excavation of channels, and building of embankments and dams. For example, hydraulic engineering can promote the use of a water body, flood protection or land drainage. Nature-based hydraulic engineering improves the management and protection of water bodies.

• Hydraulic structure

  A hydraulic structure is an embankment, stream deflector, pipe, dam or other structure intended, for example, to promote flood protection, land drainage or the use of a water body.

• Hydrological model

  A hydrological model is a mathematical representation of how water travels in a lake and river system and its catchment. The model describes the entire water cycle from rainfall into the ground and water bodies, and finally evaporation and runoff. The model and water data can be used to simulate and predict the flows and water levels of rivers and lakes.

• Hydrology

  Hydrology is a branch of geophysics that examines the presence and properties of water and the water cycle on the Earth.

• Hydropower

  Hydropower is a form of energy production in which water flow and height differences are used to produce electricity. The share of hydropower in all energy production in Finland varies from three to four per cent.

• Hygienic quality of water

  The hygienic quality of water refers to a microbiological assessment of whether the water is safe to use. The indicator of hygienic quality is the concentration of certain faecal bacteria in the water.

I

• Ice jam

  Ice jams occur in streams and rivers in winter or spring. Ice jams are typically formed when river ice melts and ice floes and ice blocks build up in a river. The ice jam slows down the flow of the river and causes flooding. Ice jam floods occur in some river stretches almost every spring. Ice cutting is one way of preventing ice jams.

• Ice lens

  In addition to the temperature, the melting of the frost in spring is influenced by such factors as snow cover, terrain type and soil type. Melting takes place both upwards from the bottom of the frozen layer and downwards from the ground surface. When some frozen areas remain under the thawed surface soil, these frost deposits are called ice lenses.

• Indicator species

  An indicator species (index organism) is a species whose occurrence indicates certain characteristics of a habitat. The indicator species’ habitat requirements may be particularly specific, or the organism may be highly sensitive to certain environmental changes.

• Infiltration

  Infiltration is a process where water enters the soil from the surface and moves downwards. Infiltration also refers to the deliberate introduction of wastewater, stormwater or other water into the ground.

• Infiltration amount

  Infiltration amount is the volume of rainwater that is filtered by the soil (mm).

• Infiltration rate

  Infiltration rate is the rate at which water infiltrates into the ground (mm/h).

• Infiltration swale

  An infiltration swale is a low-lying area or a trench with gently sloping sides that is usually dry and covered with vegetation. Stormwater may temporarily accumulate in an infiltration swale and be infiltrated into the ground within a short period of time.

• Inspection pipe

  An inspection pipe is a vertical pipe installed in an individual pipeline to facilitate inspections and maintenance of the pipe system. Inspection pipes are installed at regular intervals in wastewater and stormwater sewers.

• Internal load

  Internal load, or internal loading, refers to a situation in which phosphorus previously bound to the bottom sediment is released back into the water. Internal loading may occur especially when algae growth increases, a large amount of algae sinks to the bottom, and the surface of the bottom sediment becomes anoxic. Internal loading is often a result of heavy external loading.

• IPCC

  The IPCC (Intergovernmental Panel on Climate Change) is an intergovernmental scientific expert body established in 1988 to support policy making on climate change. The IPCC’s task is to gather and evaluate scientific information on anthropogenic climate change and its impacts.

• Iron bacteria

  Iron bacteria are bacteria that oxidise iron. Their oxidation products may dye the water of a brook or a ditch brown. Iron can also rise to the surface, forming an oily film.

J

• Joint property management association of a water area

  A joint property management association of a water area consists of property owners who have a share in a shared water area. When a person acquires a property of this type, they will automatically become a member of the association.

K

• Keystone species

  A keystone species is one that offers food, shelter or a substrate for many other species. The decline or disappearance of a keystone species can consequently have far-reaching consequences. Keystone species in the Baltic Sea include the bladder wrack, common eelgrass and bay mussel, whereas in freshwater ecosystems certain water fleas and submerged macrophytes are examples of keystone species.

L

• Lake outlet

  The outlet is the point in a lake where the waters are discharged downstream. The outlet determines the water level of the lake, which can be altered by making the outlet deeper or shallower. The outlet of a regulated lake has a dam.

• Lake percentage

  The lake percentage refers to the total percentage of lake surface in a catchment.

• Lake restoration

  Lake restoration refers to measures aiming to improve the ecological status of a lake that has undergone eutrophication or is otherwise degraded. The most important measure is to reduce the external nutrient loading. In-lake restoration measures to inhibit internal loading may include, for example, intensive fishing of cyprinid fish (biomanipulation), oxygenation during winter and, in rare cases, chemical precipitation.

• Lake turnover

  Lake turnover refers to the complete mixing of the water masses of a lake during spring and autumn which breaks down the boundaries between different water layers. Turnover becomes possible when the surface water layers in a lake or the sea warm up or cool down, hence evening out the density differences between the layers. Finally, the wind mixes the water masses and an even temperature is reached.

• Land drainage

  Land drainage refers to moving excess water that causes damage or harm or prevents cultivation or forestry practices away from the targeted land area. Land drainage is divided into arterial drainage and field drainage.

• Leach field

  A leach or a leaching field, also called a leaching or seepage bed, is a structure intended for treating wastewater or stormwater in which water is infiltrated into the soil. A relatively large area is required for a leach field, which restricts its suitability for a small site.

• Lentic water

  Lentic water refers to water bodies with no essential flow. This means that lentic water is the opposite of flowing (lotic) water. Lentic water bodies include the sea, lakes, ponds, reservoirs and canals.

• Life cycle

  The life cycle is the entire life span of an organism with its different stages, for example starting with fertilisation, spores or eggs, until the corresponding phase of the next generation.

• Limonite

  Iron oxide deposits found at a lake bottom are called limonite or ‘lake ore’. The iron in these deposits comes from the weathering of rocks containing iron. Limonite is mainly found in the lake regions of Central Finland. Similar deposits in mires are known as ‘marsh ore’.

• Littoral zone

  The littoral zone is a relatively shallow coastal zone. The littoral zone is the part of the lake or sea foreshore with sufficient light for primary plant production.

• Load-following power

  Load-following power is energy production that is able to respond rapidly to fluctuations in demand for electricity. Load-following power is needed because storing large quantities of electricity is not possible. It also plays a role if there are disruptions to electricity production.

• Long-range transboundary pollution

  Long-range transboundary pollution is pollution caused by harmful substances from emission sources located far away, even on the other side of the globe, from which the substances are carried far and wide, usually in the atmosphere.

• Low pressure

  Low pressure is an area in which the atmospheric pressure is lower than in its surroundings. The lower the air pressure at the centre relative to its environment, the deeper the low pressure. In a deepening low pressure area, the air pressure decreases. Precipitation often occurs in low pressure areas, especially in connection with the weather fronts associated with them.

M

• Main channel

  In the Water Act, a main channel refers to the deepest section of a river which forms a channel for the free flow of water, transport, timber floating and passage of fish. A main channel may also be a strait or narrow channel in a water body that is regularly used for traffic or where fish usually pass.

• Major Baltic inflow

  A major Baltic inflow is a strong inflow of surface water from the North Sea into the Baltic Sea. It brings 200–300 km³ of saline and oxygen-rich surface water into the Baltic Sea through the Danish straits over a short period of time, or a few weeks. The highly saline water is carried along the bottom of the Baltic Sea and also mixes water in the deep parts of the sea where there normally is no mixing.

• Massive soil frost

  Massive soil frost is typical for dense soil types. It refers to uniform soil frost with no ice-free cavities or different layers of frost. Massive soil frost increases soil volume as more water rises into it and freezes during the winter.

• Maximum concentration

  Maximum concentration is the maximum permitted concentration of a hazardous or harmful substance, for example in tap water. The concept of maximum concentration is also applied to the classification of natural waters.

• Mean discharge

  Mean discharge, or mean flow (MQ), is the average discharge over a given observation period.

• Mean water level

  The mean water level (MW) is the average water level over a given observation period. It is expressed as height above sea level in some system of heights.

• Mercury

  Mercury is a long-range heavy metal that accumulates in the biota. Most of the mercury in Finnish river basins originates from atmospheric deposition resulting from such activities as the combustion of coal. The use of mercury has been restricted globally. However, it will take time before these restrictions will be reflected in mercury concentrations in fish. Water bodies that were affected in the past by mercury discharges from local industry are recovering.

• Microorganism

  Microorganism, or microbe, is a common term for all organisms that are so small that they cannot be seen with the naked eye. Aquatic microorganisms include bacteria, microscopic algae and zooplankton.

• Microplastic

  Plastic particles with a diameter of less than half a centimetre are referred to as microplastics. In waters, microplastics often end up in the bodies of organisms, and ultimately also in the food and drink of humans. Microplastics are generated from car tyres, cosmetics products and plastic bottles, for example. They end up in water bodies with stormwaters and wastewater.

• Migratory fish

  Migratory fish are fish species that hatch in streams, mature in the sea or a lake, and return to the same stream where they were hatched to reproduce. The Atlantic salmon, landlocked salmon, brown trout, eel, asp and lamprey as well as migrating forms of the Arctic char, grayling and whitefish are migratory fish.

• Minimum building elevation

  Minimum building elevation refers to the level below which structures sensitive to drenching, such as the base floor of a building, should not be placed. Minimum building elevation is primarily determined based on the flood level, but other factors are also taken into account, such as the purpose and construction of the building as well as the characteristics of the water body, including wave height. Consequently, the floor of the building should be well above the minimum building elevation.

N

• N2000 system of heights

  A system of heights defines the reference level on which the indication of all other heights is based. In Finland, the use of the N2000 height system is recommended, the reference level of which is based on European height systems. Previous Finnish systems include NN, N43 and N60.

• Natural drainage system

  Natural drainage systems are drainage arrangements for fields which ensure the drainage capacity of channels and improve water quality. For example, pollution loads to water bodies are reduced by restoring channels and by means of flood plains, flood meadows, submerged weirs and wetlands.

• Nature type

  Nature type, or habitat type, refers to a water or land area characterized by certain biotic and abiotic features. Aquatic nature types include humic lakes and large shallow sea bays, for instance.

• Nature-like fishway

  A nature-like fishway is a bypass which mimics a natural stream and through which fish and other aquatic organisms can pass a dam. A nature-like fishway promotes the spread and preservation of species in a dammed river system.

• Nitrate

  Nitrates are inorganic nitrogen compounds. Most soluble nitrogen found in water is usually in nitrate form. An exception to this are water bodies with heavy wastewater loading, which may contain large volumes of ammoniac nitrogen.

• Nitrates Decree

  The so-called Nitrates Decree (Government Decree on Limiting Certain Emissions from Agriculture and Horticulture, 1250/2014) is based on the EU Nitrates Directive (91/676/ EEC). The purpose of this decree is to prevent and reduce emissions into surface water caused by livestock production and the storage and processing of manure.

• Nitrates Directive

  The so-called Nitrates Directive (Council Directive 91/676/EEC concerning the protection of waters against pollution caused by nitrates from agricultural sources) plays an integral role in water protection regulation in the European Union. Its objective is to reduce water pollution caused by nitrates from agriculture.

• Nitrogen

  Nitrogen is an essential substance for all organisms. Nitrogen is often in short supply in nature, and providing plants with more nitrogen brings on lusher growth. In aquatic ecosystems, and particularly in the Baltic Sea, nitrogen causes eutrophication. As plants cannot use elemental nitrogen, they need nitrogen compounds: nitrates and ammonium salts. Nitrogen is carried into water bodies with wastewaters and runoff waters.

• Nutrient load

  Nutrient load, or nutrient loading, refers to the amount of nutrients, i.e. nitrogen and phosphorus, entering a water body. Nutrients can end up in water bodies from the catchment and the air, and as so-called internal load from the bottom sediments. Excessive nutrient loading causes eutrophication.

• Nutrients

  In water protection, nutrients usually refer to nitrogen and phosphorus. These two nutrients are primarily responsible for the eutrophication of water bodies. Based on their nutrient levels, water bodies are classified as nutrient-rich and nutrient-poor waters.

O

• Open channel

  An open channel refers to an open conduit of water on the ground surface in which water usually flows towards lower elevation.

• Open ditch

  An open ditch is an uncovered channel dug in the ground to drain or irrigate a certain area of land.

• Operational monitoring

  Operational monitoring refers to an operator’s duty to monitor the impacts of the pollution they cause in a water body. Operational monitoring is based on the Environmental Protection Act, and the decision on the monitoring programme is made in connection with the permit process.

• Organic carbon

  Organic carbon is one of the parameters of ambient water quality. The amount of either dissolved organic carbon (DOC) or total organic carbon (TOC) is measured. The humus content of water has the greatest impact on the DOC value, whereas the TOC value also includes carbon bound in solid matter.

• Organic matter

  Organic matter is derived from living organisms. Organic matter includes live and dead parts of plants and animals in the soil, as well as their secretions, roots, and other parts that have decomposed partly or fully.

• Outlet channel

  An outlet channel is a natural or constructed channel reserved for discharging water from a dammed reservoir, or urban stormwater or other water, into a water body or other suitable location where they cause as little harm as possible.

• Overflow discharge

  Overflow discharge is a situation where wastewater ends up in the environment from the sewer network or a pumping station. Overflow discharges occur in exceptional situations. For example, they may be caused by heavy rain, a power outage at a pumping station or a blockage in the sewer network.

• Overland flow

  Overland flow is a management method for stormwaters or drainage waters in which water is allowed to flow along a plant-covered surface.

• Overland flow field

  An overland flow field is a natural or constructed field to which the waters from a drainage area are led. The recommended area of the field is 0.5% to 1% of the catchment surface. Overland flow fields are also used to manage stormwaters.

• Oxygen content

  Oxygen content, or oxygen concentration, is one of the quality elements of surface waters. The amount of dissolved oxygen is associated with water temperature, which is why oxygen content is expressed as a saturation rate, i.e. a percentage of the ‘full’ oxygen content of water at the same temperature. Aquatic organisms need oxygen to live. Some organisms also produce oxygen in the water by photosynthesis.

• Oxygen depletion

  Oxygen depletion is a situation where so little oxygen is available in the water or on the sediment surface that the biota suffers, dies or moves away. Oxygen depletion occurs especially at the bottom layer of eutrophic lakes and ponds, either during winter or when the water is heavily stratified and bacterial activity depletes oxygen.

• Ozonation

  Ozonation (ozone treatment) is one way of disinfecting tap water. Ozonation is a favoured method because, unlike chlorination, it does not affect the taste of the water negatively. As ozone evaporates rapidly from water, its disinfecting effect does not last as long as that of chlorination.

P

• Pack ice

  Pack ice is created in the sea when drift ice is driven by wind or currents and builds up at a certain location. When ice becomes packed, it starts cracking, and the pieces are pushed up on top of each other as piles or ridges.

• Parasitism

  Parasitism is a relationship between organisms in which one species benefits at the expense of the other. The difference between parasitism and preying is that the host species of the parasite survives. The exception to this are parasitoids. In their life cycle, only the larvae are parasites and they end up killing their host.

• PBDE

  PBDEs (polybrominated diphenyl ethers) are long-range and very persistent compounds used as flame retardants. The use and import of PBDEs are currently banned in the EU, and the EU has also set strict maximum limits for their concentrations in the aquatic environment. The limit values are commonly exceeded, and they have been criticised for being too strict.

• PCB

  PCBs, or polychlorinated biphenyls, are organic chlorine compounds harmful for the environment that were previously used in capacitor and transformer oils and some other products. The use of PCBs, as well as certain other persistent organic compounds, is now strictly prohibited, for example in the European Union.

• Peak runoff control structure

  A peak runoff control structure is a weir built in a sedimentation pond that can regulate the velocity of water flow. For instance, flow may be controlled by pipes installed in the weir, in which case the weir can also be called a pipe weir. Peak runoff control can reduce the quantity of solids and nutrients bound in them carried to downstream waters, especially if the flow rate is high.

• Pelagic zone

  The pelagic or free water zone is the part of the surface or intermediate layer of the sea or a lake that is located outside the littoral zone and in which there is no large vegetation.

• Perforated casing well

  A perforated casing well, or slotted tubewell, is a tubular well immersed in the ground into which water filters through the slots in the tube walls or its bottom. The most common diameter of the tube is 40 cm, and its length varies from a few metres to 50 metres. A perforated casing well is suitable for the water supply of communities in sand and gravel areas.

• Periphyton

  Periphyton refers to algae attached to the surface of rocks, submerged logs and aquatic plants. They may be single-cell algae, including diatoms, which make the surface of a stone or a dock post slimy. The largest periphytic algae are often filamentous.

• Permafrost

  Permafrost refers to soil that stays permanently frozen. Uniform permafrost is usually found where the average annual temperature is below -5 degrees Celsius. In most cases, permafrost extends to a depth of dozens of metres, or up to one kilometre at maximum, unless it reaches the bedrock first.

• Permeable surface

  Unbuilt or built surface where rainwater is infiltrated into the ground, for instance sand or grass.

• pH value

  The pH value describes the acidity of water or other liquids. It is expressed on a scale of 0 to 14, where 7 is neutral, and values lower than 7 indicate that a liquid is acidic, and values higher than 7 that it is alkaline. The pH value is based on the activity of positive hydrogen ions in a solution. The surface waters and groundwaters in Finland are usually slightly acidic, as their pH is approximately 6.5.

• Pharmaceutical residues

  Pharmaceutical residues refer to pharmaceutical substances that are present in wastewater. They originate in toilet sewage and have ended up there through human excretions or washing water. Many pharmaceuticals can be harmful if they end up in water bodies.

• Phosphorus

  Phosphorus is an essential substance for all organisms. Lack of phosphorus limits algae growth in many Finnish aquatic systems. Consequently, a high phosphorus load causes eutrophication. The main sources of phosphorus ending up in water bodies are domestic and industrial wastewaters and runoff from fields and forests.

• Phosphorus Decree

  The Phosphorus Decree applies to the use of phosphorus in agriculture and horticulture as well as in environmental construction and landscaping. The objective of the decree is to prevent and reduce phosphorus emissions into water and soil resulting from the use of fertilisers and manure. When the decree enters into force, the fertiliser limits previously associated with the agri-environment payment schemes will apply to all farmers.

• Phosphorus filter

  The purpose of a phosphorus filter is to reduce the phosphorus load caused by domestic wastewater in sparsely populated areas. A phosphorus filter may be a structure resembling a tank or well that contains material which binds phosphorus. The wastewater is led through this material.

• Phytoplankton

  Phytoplankton mostly consists of single-cell algae that drift freely in water and obtain their energy from photosynthesis. Cyanobacteria, or blue-green algae, are also usually included in phytoplankton. Phytoplankton, together with bacterioplankton, form the foundation of the food web in aquatic ecosystems.

• Pipeline inspection well

  A pipeline inspection well, or a manhole, is a pit that enables checking that a sewer, stormwater or other drainage system is functioning properly as well as carrying out maintenance work if necessary, such as clearing blocked pipe systems.

• Pit with shut-off valve

  A pit with pipeline shut-off valve may be located in a water, storm water or wastewater drainage system. When the valve is closed, water flow stops.

• Plankton

  Plankton refers to small organisms that drift in the water mostly with the currents, or swim very slowly. Plankton is divided into phytoplankton and zooplankton, and often also bacterioplankton.

• Planktonic algae

  Planktonic algae are microscopical algae that drift in the water along its currents. Planktonic algae are mostly single-cell organisms. They perform photosynthesis, produce oxygen in the water and form part of the foundation of the aquatic food web.

• Plant nutrient

  Plant nutrients are substances that plants need in order to grow. The most important plant nutrients are nitrogen, phosphorus and potassium. Of these, nitrogen and phosphorus cause eutrophication when they end up in water bodies.

• Point source pollution

  Point source pollution refers to pollution loading of water bodies from individual sources that can be measured. Point source pollution includes emissions from municipal and industrial wastewater treatment plants.

• Pollution load

  Pollution load, or loading, refers to the amount of polluting substances entering a water body. The nitrogen load, for example, is the amount of nitrogen compounds entering the water body from the catchment and air. The pollution load is often divided into point and non-point source pollution.

• Precipitation

  Precipitation, or rainfall, indicates the amount of water falling onto the ground in different forms within a certain time. One millimetre of precipitation means that one litre of water corresponding to a one-millimetre-thick layer has fallen on an area of one square meter.

• Preliminary assessment of flood risks

  Preliminary assessment of flood risks refers to an assessment of the flood risks in an area based on actual floods and available information on the development of climatic and hydrological conditions. Potential significant flood risk areas are identified based on these assessments.

• Process water

  Process water refers to water used by industrial plants in their production processes. Process water usually needs to be treated before it is discharged into a water body.

• Profundal zone

  The profundal zone is the bottom of a lake or sea. Its depth is such that not enough light reaches it for plant production.

R

• Radon

  Radon is a radioactive gas that has no smell, taste or colour. It dissolves in water and can easily evaporate from water into air. Radon breaks down into other radioactive isotopes. It occurs naturally in groundwater, especially in bedrock groundwater. There may be major variations in the radon concentrations in water from drilled wells, even between wells located close to each other.

• Rain garden

  A rain garden is a low-lying area with plant cover into which stormwaters can be led. The water is retained and cleaned in this area, from which it is infiltrated through a soil layer into the ground or led into a stormwater system.

• Rain shower

  A rain shower is a short and intense burst of rain that usually originates in a cumulonimbus cloud. A shower may also bring hailstones or snow.

• Rainfall

  Rainfall, or precipitation, indicates the amount of water falling onto the ground in different forms within a certain time. One millimetre of precipitation means that one litre of water corresponding to a one-millimetre-thick layer has fallen on an area of one square meter.

• Rating curve

  The rating curve describes the ratio of water level and volumetric flow rate in a channel. The rating curve is obtained by measuring volumetric flow rates at different water levels. Once the rating curve has been obtained, the flow rate can be calculated based on water level observation.

• Raw water

  Raw water is water that industrial plants and communities abstract from a surface water or groundwater source. Raw water often needs to be treated before it is suitable for use as industrial process water or for distribution in the water supply network.

• Reference period

  A reference period is a 30-year period used in climate studies. The average figures of an individual year, including the average temperature, are compared to this long-term average. The most recent reference period runs from 1981 to 2010.

• Regulated lake

  A regulated lake is a lake whose water level and flow are regulated by means of dams or other regulation structures. Around one third of Finnish lakes’ surface area is regulated.

• Regulating dam

  A regulating dam is a dam structure used to regulate volumetric flow rate and thus the level of water. The regulating dam can, for example, be used to slow down the flow of water in a channel or to create wetlands. Among other things, regulating dams are used in catchment water management and in stormwater systems.

• Regulation permit

  A permit to regulate a water body is granted by the Regional State Administrative Agency. When considering a new regulation permit, the Regional State Administrative Agency takes into account both the need for regulation and its benefits and disadvantages. Many old permits granted by other authorities are still in force.

• Regulator well

  A regulator well is a well connected to a subsurface drainage system used to regulate subsurface drainage runoff and thus the level of groundwater.

• Reservoir

  A reservoir is an artificial water body built or dammed by humans. Reservoirs often serve as water stores for hydropower plants. The largest reservoirs in Finland are Lokka and Porttipahta in Sodankylä.

• Residual risk

  Residual risk usually refers to potential flood damage which cannot be prevented, or the prevention of which is not feasible for technical or economic reasons. Residual risks are those potential harms caused by a flood that remain when flood protection is set at an acceptable level.

• Restoration of small water bodies

  The aim of the restoration of small water bodies is to improve the status of brooks, ponds, springs and other small water bodies. The restoration methods vary depending on the site. If the channel of a brook has been cleared in the past, returning rocks and wood into the channel is an important restoration measure.

• Restoration plan

  A restoration plan is a written document concerning a water body restoration project. It shows which restoration measures will be carried out in a water body, what the aim and schedule is and how they will be funded. The restoration plan can be thought of as a script for a restoration project.

• Retention

  Retention is a water management term. Its purpose is to section surface runoff over a longer period.

• Retention basin

  A retention basin is a basin intended for retaining stormwaters, and it only has water some of the time.

• Return period

  Return period, or recurrence interval, is the average time after which a flood of a certain size or greater recurs. However, floods do not occur regularly. For example, a return period of 250 years means that a flood is likely to occur four times over a thousand years. The annual probability for the occurrence of a flood of this magnitude is 0.4%.

• River

  The Water Act defines a river as a water body with flowing water whose catchment covers at least a hundred square kilometres.

• River and lake system

  A river and lake system, or water course, refers to a system of inland waters that discharge into the sea through the same river.

• River basin

  A river basin is an area from which all runoff waters flow into the sea through a brook, lake, river or estuary.

• River basin district

  A river basin district is an area consisting of one or more river basins for which water resources management plans are drawn up. There are eight river basin districts in Finland.

• River basin management planning

  The purpose of river basin management planning is to protect and improve the status of aquatic ecosystems. The Act on the Organisation of River Basin Management 1299/2004 implements the European Union Water Framework Directive in Finland.

• Roof water

  Roof water is rain and meltwater running down the roofs of buildings.

• Runoff

  Runoff indicates the volume of water moving on the ground surface and in the soil. Snowmelt and heavy rain increase this volume and may cause floods.

S

• Sea state

  Sea state refers to the general wave conditions on the surface of the sea or a lake where the size of individual waves varies. The most important factors affecting the rising of waves are wind speed and duration as well as the fetch, or the distance from the upwind shore. The main parameters used in describing sea state are significant wave height, wave direction, and wave period.

• Sediment

  Sediment refers to solid materials that are transported and deposited by water, such as fine sand or clay. As the water flow decreases, the sediment settles to the bottom, where thick beds of sediment accumulate over the years. The thickness of lake sediment is usually 2 to 10 metres. The sediment materials can start moving again if the flow increases.

• Sedimentation pit

  A sedimentation pit is a water protection structure used in ditch network maintenance. It is a wider and deeper part of a field ditch with a volume of 1 to 2 m³. The sedimentation pit aims to retain solids carried by water during digging operations, hence preventing them from being transported to the downstream water body. However, no research data exists to support their efficiency.

• Sedimentation pond

  A sedimentation pond is a water protection structure of drainage operations. It is often associated with an outlet ditch into which the waters of an upstream catchment are directed. The purpose of sedimentation ponds is to reduce the quantity of suspended solids and particulate nutrients in water. Sedimentation bonds slow down the water flow velocity, causing the solids to settle into the bottom.

• Seepage area

  A seepage area is an area of land where groundwater seeps onto the ground surface with no clear discharge area or other open water surface.

• Seiche

  A seiche is a standing wave in an enclosed water body. For example, seiches can occur in lakes or in the Baltic Sea as a result of wind, gravity and rebound from the shores. On the shores of the Baltic Sea, a seiche raises and lowers the sea water surface in periods of approximately 24 hours.

• Separate sewer system

  A separate sewer system is a pipe system in which sewage and stormwaters are kept separate.

• Septic tank

  A septic tank is a tank intended for treating wastewater in which the solids contained in the wastewater settle down to the bottom. In former times, septic tanks were commonly used for wastewater treatment in sparsely populated areas, but their cleaning efficiency is poor. Today septic tanks are only used for the pre-treatment of wastewater, and the actual treatment is carried out in some other system.

• Sewage sludge

  Wastewater sludge, or sewage sludge, is sludge generated at sewage treatment plants. Sludge is generated when solids are removed from the wastewater and dissolved impurities are precipitated. Wastewater sludge can be used for energy production or, for example, in landscaping.

• Shoreline restoration

  The objective of shoreline restoration is to improve the status of a shoreline area. The most common reasons for restoration are eutrophication and plant overgrowth. In these circumstances, the most important measure is reducing the nutrient load from the catchment. Other possible measures include emergent plant removal.

• Significant flood risk area

  An area where the flood risk may be significant on the basis of a preliminary assessment is designated a significant flood risk area. In this assessment, the likelihood of flooding and the harmful consequences of a flood are taken into consideration. The significance of the consequences is assessed in general. A flood hazard map and a flood risk map as well as a flood risk management plan are prepared for a significant flood risk area.

• Significant wave height

  Significant wave height is calculated based on the measured wave height distribution. The result corresponds to an experienced seafarer’s visual estimate of the wave height. Significant wave height is approximately the same as the average height of the highest one-third of all waves. Maximum wave height is almost twice the significant wave height.

• Sliming

  Sliming most often refers to the soiling of fish traps in water. Sliming is mainly caused by microscopic algae that adhere to the trap structures. Eutrophication usually increases sliming, but sliming can also occur in nutrient-poor brown water lakes.

• Slush ice

  Slush ice, or white ice, is frozen slush. Slush ice is formed when snow presses down on the ice cover of a lake, causing water to rise on top of the ice. When the temperature drops, the snow slush freezes into slush ice. Its load capacity is only one half of the load capacity of clear ice or black ice.

• Small water body

  Small water bodies include brooks, ponds, streamlets, ditches and springs as well as small fladas and glo lakes. Small water bodies are sensitive, which means that even small changes in their close surroundings can impair their status.

• Snow depth

  Snow depth describes the thickness of the snow layer. The accumulation of snow varies according to the terrain, which means that snow depths differ in open areas and in the forest. Snow depth can be measured both automatically with ultrasound and by means of a stick with a measurement scale.

• Snow load

  The snow load indicates the weight of the snow layer in kilograms per square metre. This is the same as the amount of water in the snow: the thickness in millimetres of the water layer that would be produced if the snow were melted. The snow load, or water equivalent, depends on the density and depth of the snow.

• Snow water equivalent

  The snow water equivalent refers to the amount of water contained in snow. The water equivalent unit is kg/m² (snow load). Its value corresponds to the water content of snow in millimetres.

• Soakaway

  A soakaway, also called a seepage or leach pit, is a pit for infiltrating stormwater or other water filled with aggregate or some other material with large void volume. The water directed to the pit is stored in the cavities and slowly infiltrates into the surrounding soil. The pit can also be located completely underground, in which case the water enters it through stormwater or subsurface drains.

• Soil filtration system

  A soil filtration system is one option for treating wastewater in sparsely populated areas. It is based on biological activity on the surface of the filtration sand. The filtration system must be designed for the volume of waters to be treated and the available space.

• Soil frost

  Soil frost, or ground frost, refers to a soil layer that hardens as the water contained in the soil freezes. Soil frost formation and depth and the duration of the frost season depend on the temperatures, snow cover and ground water level during the winter.

• Soil infiltration

  Soil infiltration is a simple way of treating wastewaters in sparsely populated areas. It can only be used for small volumes of wastewater which do not include toilet sewage. The soil must also be suitable for infiltration.

• Soil moisture

  Soil moisture describes the volume of water bound to the soil. Factors that influence soil moisture are soil type, precipitation, temperature, melting of snow, evaporation and water used by vegetation.

• Soil water

  Soil water is water trapped or moving freely in soil above the groundwater surface.

• Spring complex

  A spring complex refers to a connected area of land with groundwater influence, which may include open water springs, spring-fed brooks and streamlets as well as seepage areas.

• Stage

  Stage is a hydrological concept which is used to describe the water level in rivers. Factors that affect the stage of rivers include precipitation, runoff and evaporation as well as flows from the lakes of the river basin.

• Stormwater

  Stormwater is water from rain and snowmelt flowing along streets and property surfaces. Stormwaters must be managed. The primary aim is to infiltrate stormwaters into the ground or to manage them at their point of origin. If this is not possible, stormwaters are directed to a stormwater sewer, separate from wastewater sewers.

• Stormwater basin

  A stormwater basin is a basin used or built for storing or retaining stormwaters.

• Stormwater drain

  A stormwater drain, or rainwater sewer, is a sewer that is separate from wastewater sewers. It leads away rain and drainage water accumulated in yards, subsurface drains and streets. From the stormwater drains the water is discharged into a water body.

• Stormwater drainage system

  A stormwater drainage system is a system consisting of structures intended for managing stormwaters.

• Stormwater drainage well

  A stormwater drainage well is a well for collecting stormwaters. The well may be covered by a grid. It may also have a soil or sand filter.

• Stormwater fee

  A stormwater fee is charged for conveying stormwaters into a sewer.

• Stormwater flood

  A stormwater flood occurs when it rains so heavily that the city’s stormwater system is overloaded. This means that the rainwater sewers are unable to carry the rainwater at a sufficient rate and the water rises up to the streets and yards, sometimes causing major damage.

• Stormwater infiltration structure

  A stormwater infiltration structure is a system designed to promote the infiltration of stormwaters through soil layers into the ground.

• Stormwater management

  Stormwater management refers to measures that control stormwater accumulation or are associated with leading away and treating stormwaters.

• Stormwater network

  A stormwater network is a pipe network for moving away stormwaters and drainage water from building foundations. The stormwater network may consist of drain pipes and possibly also open channels directly connected with them. The network also includes stormwater drainage wells and possible pumping stations.

• Stormwater pond

  A stormwater pond is a structure for collecting, retaining and cleaning stormwater. Stormwaters are directed to a stormwater pond either as surface runoff or through a stormwater wetland, or an infiltration and filtering structure. Stormwater ponds also add variety to the landscape.

• Stream

  Stream, or lotic water, is a general concept that covers all water bodies that flow in a channel, or rivers, brooks, streamlets and ditches.

• Stream restoration

  The purpose of stream restoration is to achieve and safeguard the good ecological status of a river or other flowing water body and to promote the natural reproduction of migratory fish. Restoration measures may include improving spawning grounds, removing barriers to fish migration or building bypass channels.

• Streamlet

  The Water Act defines a streamlet as a channel smaller than a brook whose catchment is less than ten square kilometres where water does not flow continuously and the passage of fish is not possible to any significant extent.

• Sublittoral zone

  The sublittoral zone is the shoreline zone below the lowest water level that is always covered with water.

• Submerged macrophyte

  Submerged macrophytes are plant species that complete their entire life cycle submerged under water. Only its flowers may rise above the surface.

• Submerged weir

  A submerged weir is a dam structure or sill constructed below the water surface. It can be used to raise the water level of a lake or channel, and also to diminish flow in drainage areas. A series of submerged weirs constructed with natural stones or gravel in a stream mimics the cascades of natural rapids.

• Sulphur Directive

  The EU Directive (2012/33/EC) known as the Sulphur Directive regulates the sulphur content in ships’ fuel. As the directive entered into force in 2015, it only applied to certain sea areas, including the Baltic Sea. In 2020, the directive’s scope was extended to all EU marine areas. The directive has led to a significant reduction in sulphur emissions from shipping in the EU.

• Surface run-off

  Surface run-off is the amount of rainwater (mm) that, rather than being infiltrated into the ground, flows along the surface.

• Surface water

  Surface water is water that flows or is stored above the ground. Surface waters include lakes, ponds, rivers and coastal waters.

• Surface water status

  Surface water status refers to the ecological or chemical status of a water body, usually both. Surface waters are classified into five status categories based on their ecological and chemical characteristics.

• Surface water temperature

  Surface water temperature describes thermal conditions in the surface layer of water (20 cm). The water temperature is influenced not only by the size of the water body but also by air temperature and wind conditions.

• Suspended solids

  Suspended solids are solid particles in water, such as clay, silt or sometimes particulate organic carbon. The metric for solids in water is turbidity.

• Swimmer’s itch

  Swimmer’s itch is a complaint caused by parasitic cercariae. You can get these larvae while swimming, especially in shallow shore areas with vegetation. The larvae, which normally are bird parasites, mistakenly penetrate the surface layer of human skin. The larvae do not reproduce in humans, and the problem clears in about a week. Showering and drying yourself with a towel after swimming reduces the risk.

• System of heights

  A system of heights (or a height system) defines the reference level on which the indication of all other heights is based. In Finland, the use of the N2000 height system is recommended, the reference level of which is based on European height systems. Previous Finnish systems include NN, N43 and N60.

T

• Tapeworm

  The tapeworm (flatworm) is a parasite of mammals that eat fish. Humans can get a tapeworm by eating raw or inadequately cooked pike, perch, ruffe or burbot, or their roe. Freezing for at least 4 days (at -18°C) destroys the larvae, after which fish and roe can be eaten uncooked. Few infestations are detected in Finland today, that is less than 50 cases per year.

• The Flood Centre

  The Flood Centre is a service jointly provided by the Finnish Meteorological Institute and the Finnish Environment Institute. The Flood Centre predicts and gives warnings of floods and maintains a continuous situational awareness related to them.

• Thermocline

  Thermocline and halocline are vertical layers in a lake or sea where some characteristic of the water changes rapidly in the vertical direction. The layer in which water temperature changes rapidly is called a thermocline, and the layer in which salinity changes rapidly is known as a halocline. The thermocline or halocline prevents the epilimnion above it from mixing with the hypolimnion below it.

• Threatened species

  A threatened species is a species whose unaided survival in nature is at risk as referred to in the Nature Conservation Act. The threatened status of species in Finland is assessed based on international criteria (IUCN) every ten years, and the Red List of Finnish species is compiled on the basis of the results.

• Tides

  Tides are periodic fluctuations in sea levels caused by the gravitational pull of the Moon and partly also the Sun. Tides in the Baltic Sea are insignificant as the water volume is relatively small.

• Total nitrogen

  Total nitrogen refers to all nitrogen found in water: nitrogen bound in organic matter as well as dissolved nitrogen. Most of this nitrogen in water is usually in nitrate form. Other forms of soluble nitrogen are nitric nitrogen and ammoniac nitrogen.

• Total phosphorus

  Total phosphorus refers to all phosphorus found in water: phosphorus bound in soil particles and organic matter as well as dissolved phosphorus.

• Transboundary river basin

  Transboundary river basin refers to a water body that extends to both sides of a state border. Finland shares river basins with Sweden, Norway and Russia. The management and use of these water bodies is based on treaties between the relevant states.

• Transboundary river basin commission

  A transboundary river basin commission, or transboundary water commission, is an intergovernmental body dealing with the management and use of water bodies extending to both sides of a state border. The commission’s work is based on a treaty between the relevant states.

• Turbidity

  Turbidity is one of the parameters of water quality. Solids in water, including soil particles, are the main cause of turbidity. Rivers in regions with clay soils often have relatively high turbidity, especially if the catchment contains large areas of arable fields.

• Two-stage channel

  A two-stage channel consists of a deeper main channel and flood plains on one or both of its sides. The main channel has water throughout the year. During a flood event, the water rises onto the flood plains in a controlled manner. The main benefits of two-stage channels are reduced flooding and improved water quality and ecology.

U

• Upstream

  Upstream refers to the parts of a river or river basin that are above a certain point, in other words close to the upper reaches or headwaters of a river. Similarly, downstream refers to the waters below a certain point, which are closer to the discharge point of a river.

• Urban flood

  Urban floods are caused by heavy rainfall, fluvial flooding or coastal flooding as water builds up in streets, yards and other areas, from where it discharges uncontrollably and causes damage.

V

• Vaporisation

  Vaporisation is the process by which water becomes water vapour at a temperature below the boiling point. During vaporisation, a heavier substance (water) becomes lighter (vapour). The reverse phenomenon of vaporisation is condensation.

• Virtual water

  Virtual water, or hidden water, refers to the amount of water contained in products. Virtual water includes all water consumed during the product’s life cycle from raw material production until the product is treated as waste.

W

• Waste dam

  A waste dam is a basin or pond formed by a dam structure that prevents the spreading of a liquid or substance behaving like a liquid. Waste dams are used in mines and the forest industry, for instance.

• Wastewater treated on site

  In sparsely populated areas, wastewaters may be processed at the point of origin rather than being led into the public sewage network.

• Wastewater treatment system

  Wastewater treatment system refers to a method and equipment used to collect wastewater, convey it to a treatment plant and treat it. A property located outside the sewage network has different options for treating wastewater: a sealed tank that must be emptied periodically, soil filtration, soil infiltration or a domestic treatment plant.

• Water and wastewater services

  Water and wastewater services are an important basic function of society. The purpose of water services is to safeguard access to clean and high-quality tap water and provide appropriate treatment of wastewater.

• Water body

  A water body is a concept used in water resources management that refers to a lake or another distinct body of water. According to the definition given in the EU Water Framework Directive, a “body of surface water means a discrete and significant element of surface water such as a lake, a reservoir, a stream, river or canal”. In the Water Act, a water body refers to a lake, pond, river, brook and other natural water area as well as a reservoir, channel and other similar artificial water area.

• Water co-operative

  A water services co-operative, or a water co-operative, is a water utility owned and managed by residents in the form of a co-operative. Water co-operatives usually operate in sparsely populated areas.

• Water distribution area

  The Health Protection Act contains provisions on water distribution areas. A water distribution area refers to a uniform part of a water distribution network where the quality of tap water is more or less constant and where a single plant is responsible for the supply of water. A water distribution area also includes the water users connected to the network in question.

• Water footprint

  The water footprint refers to the volume of water consumed by, for instance, a person or a state both directly and through the commodities they attain covering the commodities’ entire life cycle. A water footprint can also be calculated for products and services.

• Water Framework Directive

  The Water Framework Directive, or directive establishing a framework for Community action in the field of water policy 2000/60/EC, is a European Union directive that harmonises water protection in the Member States.

• Water hardness

  Water hardness describes the quantity of calcium and magnesium ions in water. The higher the quantity of these ions in water, the harder the water. Water hardness varies from area to area depending on the local bedrock and soil. While water in Finland is usually soft, in limestone areas it is hard.

• Water level

  The water level describes the fluctuations of the surface level of water in the sea and lakes. Factors that affect the water level in lakes include precipitation, runoff, evaporation as well as flows entering and leaving a lake. Factors primarily affecting the water level in the Baltic Sea include currents through the Danish straits, wind conditions, atmospheric pressure and the ice situation.

• Water level regulation

  Water level regulation refers to changing water levels and volumetric flow rates using dams or hydropower plant structures.

• Water protection association

  There are two types of water protection associations: large regional ones and smaller local ones. Local associations usually work to promote the protection or restoration of a certain water body. Regional associations have a larger field of operation, and they may also offer lake monitoring and expert services.

• Water quality

  Water quality is an indication of how suitable the water is for its intended use, for example as tap water. In the context of natural waters, water quality is an important element when assessing the status of a water body and its need for restoration.

• Water scarcity

  Water scarcity refers to a situation where water is consumed excessively in proportion to the renewable water resources that are available.

• Water Services Act

  The objective of the Water Services Act, which was passed in 2001 and subsequently updated, is to ensure access to a sufficient amount of good-quality tap water and provide appropriate treatment of wastewater. Among other things, the act sets out when a resident must join water supply and sewer networks.

• Water services operating area

  The operating area of water services is the geographic area determined by the municipality in which water utilities provide water services.

• Water Stewardship Commitment

  A Water Stewardship Commitment is a pledge made by a company or some other organisation to develop the sustainable use and management of water in its production chain. Water stewardship commitments are part of Finland’s and Finnish companies’ ambition to reach the highest level of water responsibility in the world by 2030.

• Water storage dam

  A water storage dam, or a watercourse dam, is a structure that dams water for the needs of flood protection, hydropower production or fish farming, for instance. Some of these dams regulate the stage and discharge of rivers and lakes.

• Water temperature

  Water temperature is one of the basic measurements in limnology. Temperatures measured at different depths provide information about the thermal layers in a lake or the sea. The temperature is also significant when assessing oxygen saturation in water, for instance.

• Water transparency

  Water transparency describes the transparency and opacity of water and may also reflect its level of eutrophication. A round white disk (called a Secchi disk) of a diameter of 20 cm is used to measure water transparency. The disk, which is attached to a shaft or string, is lowered into the water, and the depth at which the disk can no longer be seen from the surface is indicated by a scale on the shaft.

• Water utility

  Under the Water Services Act, a water utility is defined as a plant which manages the water services of a community in an area of operation approved by the municipality.

• Water utility report

  A water utility report is a report obtained from the water services information system (VEETI) on the operation of a water utility. Various water utility reports containing different information can be produced. Among other things, the reports include key figures describing water services and financial data.

• Wave height

  In the context of waves in the sea or a lake, wave height refers to the height difference between the trough and crest of the wave. As the height of successive waves varies, the concept of ‘significant wave height’ has been developed and adopted.

• Wavelength

  Wavelength is the distance between the crests of two successive waves.

• Weather front

  A weather front is the boundary between two different air masses. At a cold front, the colder air pushes itself under the warmer air mass, and showers typically occur in this area. At a warm front, more continuous rain is typical. A front usually moves at a speed of 20 to 50 km/h, and when the front passes over, the wind direction and temperature change.

• Wetland

  Wetland is a common term for habitats that are covered by water during most of the year and also contain aquatic and wetland vegetation at other times. Due to their ecological value and benefits for water protection as well as hunting, wetlands have been restored and built in agricultural and forest areas and cities alike. Wetlands may level out flood flows.

• Winter drawdown

  Winter drawdown is a concept related to the regulation of water bodies. It means that the water level in a lake is lowered during winter and in early spring to make space for snow meltwater. In recent years, there has been less need for a winter drawdown as snow amounts have decreased, especially in Southern Finland.

Z

• Zooplankton

  Zooplankton consists of animals that drift or move slowly in water, most of which are microscopic. For example, zooplankton includes protozoa, rotifers and crustaceans. Their main food source is phytoplankton, bacteria and smaller zooplankton. Zooplankton is an important food source for fingerlings and certain adult fish as well as for some waterfowl.