Archive of Blue-green algae bulletins

Note: This is an archived report.
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Published 24.8.2023

Calm weather has increased surface blooms of blue-green algae

There have been observations of blue-green algae in almost all of Finland this week. Although the number of observations has increased, the situation remains typical in inland waters and coastal areas. There have also been observations of blue-green algae mixed with water and floating on the surface in sea areas.

Although the number of blue-green algae blooms has increased both in lakes and coastal areas, the situation is currently typical of the time period. Calm weather enables the formation of blue-green algae surface blooms. Additionally, unstable, rainy and windy weather may have brought more nutrients to blue-green algae from the catchments and the bottom sediment. Wind has also driven blue-green algae surface blooms to the shore in places.

Very abundant blue-green algae has been observed at two observation sites of the national blue-green algae monitoring, and abundant blue-green algae at 14 observation sites. There is some blue-green algae at 33 observation sites. Additionally, 20 observations have been made by citizens, 12 of which have been found to concern blue-green algae. Currently, blue-green algae blooms have been observed in almost the entire country, including Northern Ostrobothnia.

Blue-green algae mixed with water have been observed in the southern Bothnian Sea and the Sea of Åland. There have been observations of blue-green algae mixed with water and on the surface in the eastern parts of the Gulf of Finland. Cloudy weather has prevented satellite observations of the main basin of Gotland and the western parts of the Gulf of Finland.

In late summer, blue or turquoise decomposing blue-green algae may appear on the shore as blue-green algae surface blooms die. Decomposing blue-green algae may emit an unpleasant odour. In late summer, there might also be reddish or rusty colouring on the surface. This is caused by Chrysomyxa ledi, spruce needle rust fungus.