Archive of Blue-green algae bulletins

Note: This is an archived report.
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Published 3.7.2025

Slight increase in blue-green algae observations in inland waters, coastal areas and open sea areas in the Gulf of Finland

The blue-green algae situation in inland waters progresses in the manner typical of midsummer, while slightly less algae than usual have been observed in coastal areas. However, blue-green algae can be observed in the eastern Gulf of Finland both on the coast and in open sea areas. The high winds of the rest of the week will mix blue-green algae with water, making it difficult to detect.

Blue-green algae observations have increased slightly in inland waterways since the previous week, but they are at a level typical of midsummer. The high winds of the rest of the week will mix blue-green algae with water, making it difficult to detect the blue-green algae. Very abundant algae have not been detected at inland water observation sites in the national blue-green algae monitoring this week. Abundant blue-green algae were observed at a total of five observation sites in South Karelia, South Savo and Pirkanmaa. There have been observations of some blue-green algae at a total of 33 inland water observation sites in Southern and Central Finland.

The number of blue-green algae observations has also increased slightly in coastal areas, but there are still slightly less blue-green algae than is typical at this time of summer. Abundant algae were observed at two coastal observation sites of the national blue-green algae monitoring, in the Kymenlaakso area. Some algae have been observed at eight coastal observation sites, in Kymenlaakso, Uusimaa, Southwest Finland and Ostrobothnia.

In the open sea areas of the Gulf of Finland, there has been more blue-green algae mixed with water than last week. The weather during the beginning of the week favoured the accumulation of blue-green algae on the surface, but there have been no extensive surface blooms of blue-green algae in the western parts of the Gulf of Finland and the northern parts of the main basin. On Wednesday, on the other hand, blue-green algae were observed in some places in the surface layer of open sea areas and in some outer coastal water bodies. There are no blue-green algae observations in the open sea area of the Bothnian Sea.

In addition to official monitoring, valuable information on the blue-green algae situation is also gathered from the public. The number of observations made by citizens has increased considerably since the previous week, and a total of 331 civic observations were received this week through the Järvi-meriwiki and Vesi.fi. Windy weather may have driven blue-green algae blooms into mats in coastal waters, in which case the amount of blue-green algae may have seemed more abundant than it actually is. When making observations, it should be remembered that blue-green algae deposits may be very local and pass with the winds.