Archive of Blue-green algae bulletins

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

Published 31.8.2023

Blue-green algae situation has calmed down at sea and in lakes

The amount of blue-green algae in sea areas and lakes has clearly decreased this week. Inland waters and coastal areas no longer have any observations of very abundant blue-green algae blooms. Blue-green algae may still occur later in the autumn as the weather cools, but the blooms are usually not as strong as in summer. The weekly report provided by the Finnish Environment Institute on the national blue-green algae situation ends today.

The blue-green algae situation is currently typical of the season in both inland waters and sea areas. Very abundant blue-green algae blooms have no longer been observed at lake observation sites of the national blue-green algae monitoring. This week, abundant blue-green algae have been found at ten lake observation sites and some blue-green algae at 31 lake observation sites in almost the entire country, with the exception of the northernmost Finland.

Very abundant blue-green algae blooms have no longer been observed at coastal observation sites either. In coastal areas, abundant blue-green algae have only been observed at one national blue-green algae monitoring site on the south-western coast. Some blue-green algae still occur at 14 observation sites on the south-western coast and the southern coastal area.

This week, 21 observations have been made by citizens, seven of which have been found to concern blue-green algae.

The amount of blue-green algae has clearly decreased in open sea areas. Small amounts of blue-green algae can be observed in the Åland Sea and the easternmost parts of the Gulf of Finland.

Winds can drive blue-green algae surface blooms to coasts where blue-green algae mass dies and breaks down. Decomposed blue-green algae mass may turn blue or turquoise. As heavy blue-green algae blooms decompose, they can also emit an unpleasant odour in their vicinity.

Blue-green algae blooms may still occur later in the autumn, but as the weather cools down, blue-green algae blooms are not usually as heavy as when the water is warm in summer.

The weekly report provided by the Finnish Environment Institute on the national blue-green algae situation ends today. A summary of this summer’s blue-green algae situation will be published next week.