Archive of Blue-green algae bulletins

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

Published 31.7.2025

The number of blue-green algae observations in inland waters, coastal areas and offshore areas has decreased compared to last week. In inland waters, algae are less common than usual, and the situation has remained average in coastal and open sea areas. Still, the situation varies from region to region, and individual abundant growths have been observed in different parts of the country.

The number of blue-green algae observations in inland waters has decreased since last week, and blue-green algae are less common than is typical of the turn of July and August. Although the weather has remained calm and warm, the growth of blue-green algae has slowed down. They have consumed all nutrients in the water, and no more nutrients have been transported by rainwater from catchments or released from the bottom of the lake. However, the situation may vary locally. This week, abundant algae have been observed in three locations at inland water observation sites of the national blue-green algae monitoring in Southwest Finland, Pirkanmaa and Northern Ostrobothnia. Some blue-green algae have been observed at a total of 21 inland water observation sites, mostly in Southern, Southwest and Central Finland, but individual observations have also been made in southern Lapland.

The number of blue-green algae observations on the coast has also decreased slightly from last week, but the situation is typical of the season. This week, very abundant algae have been observed at a total of six coastal observation sites of the national blue-green algae monitoring in Kymenlaakso, Uusimaa and Southwest Finland. Some algae have been observed at 17 observation sites, mostly on the coasts of Uusimaa and Southwest Finland, but individual observations have been recorded on the coasts of Kymenlaakso, Ostrobothnia, Central Ostrobothnia and Lapland as well.

Windy and rainy weather at the beginning of the week has alleviated the blue-green algae situation in the Gulf of Finland and the southwestern sea areas compared to last week and the weekend. There were still generous algae rafts in the eastern Gulf of Finland last weekend, but the blooms have since been mixed with water. In the Bothnian Sea, blue-green algae are still predominantly mixed with water, and the number of blue-green algae is high as is typical of the time period.

In addition to official monitoring, valuable information on the blue-green algae situation is also gathered from the public. This week, observations made by citizens were obtained through the Lake-seawiki and Vesi.fi, a total of 173 observations.