Archive of Blue-green algae bulletins

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

Published 8.8.2025

The blue-green algae situation has remained calm

During the past week, the blue-green algae situation has remained calm in inland, coastal and offshore areas. Less blue-green algae have been observed in inland waters and coastal areas than typically in late summer. The blue-green algae situation has also remained stable in offshore areas, and windy weather has kept the algae mixed with water in all water areas.

The number of blue-green algae observations in inland waters has increased slightly since the previous week, but the amount of blue-green algae this week is still lower than typical in late summer. The heavy rainfall and strong winds of recent days have, in places, increased nutrient levels in lake waters and intensified blue-green algae blooms. Abundant amount of algae has been observed at six inland water observation sites, in Uusimaa, Pirkanmaa, Kainuu and North Ostrobothnia, in the national blue-green algae monitoring. There have been observations of some blue-green algae at a total of 23 inland water observation sites, mostly in Southern Finland, but also in some places of Central and Northern Finland.

The number of blue-green algae observations in coastal areas has decreased this week, and less blue-green algae has been observed than typically in late summer. Abundant algae have been observed at one coastal observation site of the national blue-green algae monitoring, in Southwest Finland. Some algae have been observed at 14 observation sites, mostly on the coasts of Uusimaa and Southwest Finland, but individual observations have been recorded on the coasts of Kymenlaakso and Åland.

In offshore areas, the algae situation has remained calm, and the winds have kept blue-green algae mixed with water. Also, the sea water has cooled down slightly, and the surface temperatures are now between 17 and 22 degrees. Some surface blooms were observed at the beginning of the week in the mouth of the Gulf of Finland and in the offshore area of the Bothnian Sea. In addition to blue-green algae, water on the coast is currently clouded by the resuspension of the bottom particles (the phenomenon of winds and waves lifting the bottom material into the water column) and the heavy flow rates of rivers after the rainfall of the week.

In addition to official monitoring, valuable information on the blue-green algae situation is also gathered from the public. This week, a total of 42 observations made by citizens were obtained through the Lake-seawiki and Vesi.fi.

This year’s weekly reports on the blue-green algae situation prepared by the Finnish Environment Institute will end on 7 August, but the national monitoring of blue-green algae will continue until 30 September. Blue-green algae typically still occur in inland waters and sea areas well into the autumn. In the future, the Finnish Environment Institute will provide information on the blue-green algae situation as needed.