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The maps show the blue-green algae situation as observations from around 400 observation points, most of which are public bathing areas. The situation at the observation points is assessed once a week. Citizens can also report their blue-green algae observations and, using the Havaintolähetti app, set up their own observation points. Please note that the algae situation at an observation point may change rapidly, for example with the weather. Blue-green algae may produce different algal toxins. You should not swim in water containing blue-green algae, or allow your pets to go into it.

Blue-green algae situation 31.8.2023

Blue-green algae situation has calmed down at sea and in lakes

The amount of blue-green algae in sea areas and lakes has clearly decreased this week. Inland waters and coastal areas no longer have any observations of very abundant blue-green algae blooms. Blue-green algae may still occur later in the autumn as the weather cools, but the blooms are usually not as strong as in summer. The weekly report provided by the Finnish Environment Institute on the national blue-green algae situation ends today.

The blue-green algae situation is currently typical of the season in both inland waters and sea areas. Very abundant blue-green algae blooms have no longer been observed at lake observation sites of the national blue-green algae monitoring. This week, abundant blue-green algae have been found at ten lake observation sites and some blue-green algae at 31 lake observation sites in almost the entire country, with the exception of the northernmost Finland.

Very abundant blue-green algae blooms have no longer been observed at coastal observation sites either. In coastal areas, abundant blue-green algae have only been observed at one national blue-green algae monitoring site on the south-western coast. Some blue-green algae still occur at 14 observation sites on the south-western coast and the southern coastal area.

This week, 21 observations have been made by citizens, seven of which have been found to concern blue-green algae.

The amount of blue-green algae has clearly decreased in open sea areas. Small amounts of blue-green algae can be observed in the Åland Sea and the easternmost parts of the Gulf of Finland.

Winds can drive blue-green algae surface blooms to coasts where blue-green algae mass dies and breaks down. Decomposed blue-green algae mass may turn blue or turquoise. As heavy blue-green algae blooms decompose, they can also emit an unpleasant odour in their vicinity.

Blue-green algae blooms may still occur later in the autumn, but as the weather cools down, blue-green algae blooms are not usually as heavy as when the water is warm in summer.

The weekly report provided by the Finnish Environment Institute on the national blue-green algae situation ends today. A summary of this summer’s blue-green algae situation will be published next week.

What everyone should know about blue-green algae

Blue-green algae are at their most prolific around midsummer and in late summer. Large masses of blue-green algae in the water are a sign of eutrophication. Blue-green algae blooms hamper recreational use of waters and may produce algal toxins. You need to watch out for blue-green algae, which is why learning to recognise them is a good idea.

Recognising blue-green algae

Blue-green algae are usually only seen in the water as small, greenish specks. You cannot lift them out of the water with the stick as you can with filamentous green algae. A thick gunk of blue-green algae may build up in surface or shoreline waters. A good way of identifying them is letting some water stand in a drinking glass; if the specks rise to the surface within an hour, they are blue-green algae. The timing helps to tell blue-green algae apart from pollen: pollen is found in early summer, whereas blue-green algae typically occur in the middle and at the end of the summer.

Why should I watch out?

Some blue-green algae are toxic, but it is impossible to tell them from the non-toxic species by visual examination, and consequently you should be careful with all blue-green algae. You should never ingest water containing them, or use it in the sauna. You should also avoid bathing in the water and using it for watering any plants that you intend to eat. Do not allow your dog or other pets to drink water with blue-green algae or play around in it. Algal toxins can also make animals sick or even prove fatal to them.

Where and when?

Blue-green algae occur especially in lakes affected by eutrophication. In the Baltic Sea, blue-green algae blooms are commonly seen in the Gulf of Finland and the Archipelago Sea. When the water warms up around midsummer, the algae start proliferating. Large algae masses can appear quickly in July and August, and in calm weather they rise to the surface as algal blooms. Report your blue-green algae observations on map service or Järvi-meriwiki!

Did you know this about blue-green algae?