Archive of Blue-green algae bulletins

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

Published 3.8.2023

Unstable weather has kept the blue-green algae situation calm in lakes, surface blooms observed at sea

Somewhat less blue-green algae have been observed in lakes and coastal areas than last week, but blue-green algae may still appear mixed with water. Cloudy weather has limited satellite observations in sea areas. However, blue-green algae surface blooms have been observed in places south of Hanko and in the open sea area of the Gulf of Finland.

The unstable weather has not been favourable to blue-green algae, and the blue-green algae situation is moderate considering the season. The number of blue-green algae observations has decreased slightly since last week, both in lakes and at coastal areas. However, blue-green algae may occur mixed with water.

The national blue-green algae monitoring sites have reported very abundant blue-green algae in only one location during the past week, in Lake Suuri-Onkamo in North Karelia. There have been observations of abundant blue-green algae at seven observation sites in different parts of Finland. A small amount of algae has been observed at 15 lake observation sites.

Very abundant blue-green algae blooms have not been observed at any coastal observation sites this week. Abundant blue-green algae have been observed at three observation sites, and there are some blue-green algae at 19 coastal observation sites. Blue-green algae observations mostly take place on the southern and southwestern coasts and the Archipelago Sea.

In addition to the official blue-green algae monitoring observations, citizens have made a total of 60 observations, 34 of which concerned blue-green algae.

Clouds have made it difficult to obtain satellite observations this week. Last Friday, blue-green algae surface blooms were observed in the southern part of the Bothnian Sea and in the northern part of the main basin of the Baltic Sea, but the coverage of the observations has decreased since then.

However, blue-green algae mixed with water is still present in the Bothnian Sea, the main basin of the Baltic Sea and the Gulf of Finland. On Monday 31 July, blue-green algae surface blooms were observed in places in the open sea area of the Gulf of Finland west of Helsinki, and a larger mass occurred south of Hanko.

The information on this page was produced by the Finnish Environment Institute (Syke).