Archive of Blue-green algae bulletins

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

Published 8.6.2023

The blue-green algae situation calm both in the Baltic Sea and in lakes

The blue-green algae situation has remained calm in sea areas and inland waters, as typical in early summer. Some blue-green algae observations have been made in lakes, and at the moment blue-green algae is present at two observation sites in Southern Finland. Yellowish pollen may also be visible in water bodies and at sea, and this may resemble blue-green algae blooms.

Currently, variable, windy weather and cool water temperatures keep blue-green algae under control. The situation is typical for the time period. In early summer, abundant blue-green algae blooms rarely occur. The short warm period in May warmed the waters, and minor blue-green algae blooms occurred, in places, in lakes. At the moment, some blue-green algae are found in two lake observation sites of national blue-green algae monitoring, in Southern Finland. In the Baltic Sea, no blue-green algae blooms have been detected in satellite images.

In early summer, there may be plenty of coniferous pollen, which turns the water yellowish. Mass occurrence of pollen can be confused with blue-green algae blooms. Although blue-green algae blooms usually colour the water greenish or blueish green, yellowish blue-green algae blooms also occur. In some sea areas, pollen has also been visible in satellite images, this spring.

Blue-green algae blooms occur in waters with sufficient phosphorus nutrients. The surface blooms of blue-green algae are most common in calm weather. Wind will mix surface blooms with surface water, making it difficult to detect blue-green algae blooms. A strong or long-lasting wind, blowing from the same direction, can carry blue-green algae in the wind direction to the shores and bays. As warm water accelerates the growth of blue-green algae, blue-green algae blooms are most commonly found during the summer holidays in July-August, both in lakes and the Baltic Sea.