Water temperature 23.4.2025

Surface water temperature measurements started in lakes in the southern and central parts of Finland

Due to the early spring and ice break-off, the water surface temperature measurement season began in April in many lakes in the southern and central parts of the country. On Wednesday 23 April, temperatures of 4–9 degrees Celsius were recorded. They were close to or slightly warmer than the long-term averages. The temperatures were higher last week, but the cooler weather has caused them to drop. In the May Day week, the waters are expected to start getting warmer again. The water warms up the fastest in small and shallow lakes and in calm weather when the wind does not mix water.

The surface water temperatures are measured at the depth of 20 cm at 8 in the morning, during open water season. The measurement points are usually close to the shore. Temperatures are representative of these locations and cannot be applied to larger areas. You can view the latest observations on the water temperature map (in Finnish). Everyone can also record their own observations, making them appear on the map. The Finnish Environment Institute does not verify these observations. You can observe the general development of surface water temperatures by the colours on the map.

Further information

The information on this page was produced by the Finnish Environment Institute (Syke).

 

 

Nuori iloinen poika ui järvessä.

How is surface temperature of water measured?

The surface temperature of water varies significantly depending on the season and weather. Temperatures are measured daily in lakes, rivers and the sea during the ice-free season, and the results are available without delay.

Lakes and rivers

The surface water temperatures of lakes and rivers are measured at 34 monitoring stations, and temperature data are available from 80 sites in total. The measurements come from automated instruments placed at the depth of 20 centimetres close to the shore, and the results are available in almost real time. The official reference value is the reading recorded every day at 8:00 a.m.

Marine areas

At sea, surface water temperatures are measured from a depth of 20 to 30 centimetres using buoys. Water temperature data are also obtained from sea water level monitoring stations which operate round the year. Their measurements are taken at a depth of two to three metres, however, and the results cannot be compared to the readings from the buoys.

Fun facts about water temperature