Archive of Blue-green algae bulletins

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

Published 19.6.2025

A calm start for the blue-green algae season

As typical in early summer, the number of blue-green algae observations is moderate. Some blue-green algae have been observed in inland waters, mainly in Southern Finland. In coastal areas, even slightly less blue-green algae have been detected than typical this time of year. So far, no significant deposits of algae have been observed in offshore areas.

The blue-green algae situation in inland waters is calm, as typical in early summer. Abundant blue-green algae have been observed at two inland water observation sites of the national blue-green algae monitoring. Some blue-green algae have been observed at 15 inland water observation sites. During the past week, blue-green algae observations have mostly been made in Southern Finland, but also in Central Finland and a single observation in southern Lapland. National blue-green algae monitoring has 246 active inland water observation sites.

In coastal areas, blue-green algae observations are slightly fewer than is typical in early summer. During the past week, no abundant algae have been observed at the coastal observation sites of the national blue-green algae monitoring. Some blue-green algae have been observed at two coastal observation sites. National blue-green algae monitoring has 69 active marine area observation sites.

In offshore areas, the situation is normal for the time period. This week, unstable weather has prevented comprehensive satellite observations in the northern Baltic Sea. Small amounts of blue-green algae mixed with water have been observed in the Gulf of Finland. No blue-green algae have been observed in the Bothnian Sea, the Archipelago Sea and the Åland Sea.

At this time of summer, pollen from coniferous trees may also occur in the water, and it may resemble blue-green algae.

In addition to official monitoring, valuable information on the blue-green algae situation is also gathered from the public. This week, a total of 38 observations made by citizens were obtained through the Lake-seawiki and Vesi.fi.