Archive of Blue-green algae bulletins

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Published 22.6.2023

Blue-green algae observations increased in inland waters and at sea in Midsummer week

The blue-green algae situation in inland waters is calm as is typical of early summer, even though blue-green algae observations have increased since last week. Slightly more than average blue-green algae have been observed on the coast. Blue-green algae blooms have also clearly increased in sea areas, especially south of Porkkalanniemi and Helsinki.

The blue-green algae situation is still calm, even though the number of blue-green algae observations has increased since last week. Abundant blooms of blue-green algae have been observed at two national inland water observation sites in Southern Finland. Very abundant blue-green algae have been observed in one lake.

Some blue-green algae have been detected at 22 inland water observation sites, mainly in Southern and Central Finland, and at ten observation sites mainly along the coast of the Gulf of Finland and the Archipelago Sea. Citizens have also reported blue-green algae more often in Southern and Central Finland and South Ostrobothnia.

The situation in inland waters is typical of early summer. There have also been slightly more blue-green algae in coastal areas than is typical of this time of year. The continuously warm weather in Midsummer week may still promote the development of blue-green algae blooms, especially if the winds remain weak. Showers and thunderstorms forecast for the next few days, may also locally increase the nutrient load discharged into water systems and increase the abundance of blue-green algae blooms.

According to the current water system forecasts, the rise in the temperatures of surface waters is slowing down in surface waters in Southern Finland and Central Finland, and surface waters may cool down by more than one degree Celsius at the end of the week. Surface water temperatures will continue to rise slightly toward the weekend in Northern Finland.

The amount of blue-green algae has increased significantly in the Gulf of Finland and in the main basin of the Baltic Sea. In Finland’s open sea areas, blue-green algae have been observed in many places in satellite images throughout the Gulf of Finland. Calm conditions around the middle of the Gulf of Finland have caused algae to accumulate into surface mats. Surface algae blooms are concentrated at the outer archipelago south of Porkkalanniemi and Helsinki and at the open sea. The situation in the Bothnian Sea is still calm considering the season.