Algae bloom covers entire lake in South Savo

A massive algae bloom has completely covered Kolvosenjärvi, a lake on the border of Savonlinna and Enonkoski in South Savo, Yle reports. Authorities have banned all water use as a precaution while the algae species is identified.

Satellite images show the lake, roughly four kilometers long, nearly indistinguishable from the surrounding landscape due to the dense bloom. The phenomenon is unprecedented for the area, according to local environmental engineer Hanne Turunen, who noted that previous blooms had only affected parts of the lake.

Anja Scharf, a cottage owner who has spent 25 summers on the lake’s shore, said she and her partner had never seen such an extensive bloom. The couple has avoided using the water and may cut their planned August stay short due to the conditions.

Authorities are treating the algae as potentially toxic blue-green algae until tests confirm its type. Samples will be taken Wednesday and sent to the Finnish Environment Institute for analysis. Officials aim to determine the cause of the bloom and assess water quality this summer.

Blue-green algae can produce harmful toxins, causing symptoms such as stomach issues, skin irritation, and flu-like reactions. Authorities warn against using the water for drinking, cooking, swimming, or washing, and advise against letting animals drink or bathe in it.