Archive of Blue-green algae bulletins

Note: This is an archived report.
You can access the latest blue-green algae bulletin here.

Published 10.7.2025

The midsummer blue-green algae situation has remained moderate in most parts of the country

The number of blue-green algae observations on inland waters has decreased slightly since last week. The situation has remained stable in coastal areas, and less blue-green algae has been observed than is typical of midsummer. However, based on satellite images, slightly more blue-green algae have been observed in places in the open sea compared to last week.

The number of blue-green algae observations made through national monitoring has decreased slightly in inland waters since last week. Abundant blue-green algae have been observed at a total of four inland water observation sites in Pirkanmaa and North Savo. Some blue-green algae have been observed at 25 inland water observation sites, mostly in Southern and Central Finland, but a single observation has also been made in southern Lapland.

The blue-green algae situation in coastal areas has remained the same as last week, and less blue-green algae has been observed than is typical of midsummer. Strong wind and waves have mixed the water column and raised the bottom material to the surface, especially on the western coast. Rainfall at the beginning of the week has also brought cloudy water to the coast through rivers. Some algae have been observed at a total of ten coastal national blue-green algae monitoring sites in Ostrobothnia, Southwest Finland, Uusimaa and Kymenlaakso.

Blue-green algae that have been mostly mixed with water have been observed in the western parts of the Gulf of Finland and the main basin of the Baltic Sea more extensively than last week. On Wednesday, blue-green algae have been observed in the surface layer in the eastern parts of the Gulf of Finland and on the surface in places in coastal areas and in the open sea. Blue-green algae occur in places in the eastern parts of the Archipelago Sea and to the north of Hanko.

In addition to official monitoring, valuable information on the blue-green algae situation is also gathered from the public. This week, a total of 86 observations made by citizens were obtained through the Lake-seawiki and Vesi.fi.