Blue-green algae puts three South Savo lakes in crisis

Kolvosenjärvi is in an environmental crisis after an unusually extensive blue-green algae bloom, while two other lakes in South Savo have shown similar symptoms, Yle reports. The situation at Kolvosenjärvi has eased, but the lake’s resilience has partly collapsed and recovery could take years.

Kolvosenjärvi, located on the border between Enonkoski and Savonlinna, turned so green in late July that it was difficult to distinguish from the surrounding landscape in satellite images. The algae blooms have since diminished, and the lake’s colour now appears more normal.

Samples taken in mid-August showed that total phosphorus and nitrogen levels were clearly above their long-term averages. A new sample from a deeper part of the lake also showed that oxygen near the bottom had almost completely run out, according to Pekka Sojakka, a waterway expert at the Permit and Supervisory Agency.

Sojakka said the lake is affected by widespread low oxygen levels, which directly influence the circulation of nutrients. The lake is partly experiencing what is known as internal loading, in which nutrients are released from the bottom into the water.

The condition may be the result of combined impacts from forestry and agriculture, Sojakka said. He added that the sources of the load should be investigated and reduced as soon as possible.

“The lake’s resilience has already partly collapsed. Restoring it to a normal level will take years,” Sojakka said.

Municipalities, village associations and water protection organisations can apply for water management grants and begin restoration work independently. Individual residents, however, have limited ability to address the problem on their own, according to Sojakka.

The Permit and Supervisory Agency has also received information in recent days that Kalajärvi in Punkaharju and Toiviojärvi in Juva may be in a similar condition. The lakes have shown strong green-grey clouding for about three weeks, raising strong suspicions of extensive blue-green algae blooms.

Authorities have identified at least one factor that the lakes may share. Even less productive forest areas are now suitable for logging, and extensive logging has reportedly taken place in the areas. Sojakka said the current conditions are probably the combined result of agriculture, forestry and natural conditions.

The agency has not carried out formal toxicity tests in the area. However, the lake water may contain toxic blue-green algae, and people are advised to avoid contact with it. There is no official ban on using the lake water, but Sojakka advises caution.

Water containing blue-green algae must not be used for drinking or food preparation. It should not be used for bathing, washing dishes, watering edible plants, or as drinking or washing water for animals. Using it as sauna water may carry toxins into the lungs in the steam.

People should also avoid using the water for household purposes for several days after the algae blooms have ended. The duration of the situation remains uncertain, as blue-green algae can continue multiplying well into autumn. Authorities are monitoring the lakes.

It is not yet known whether Kolvosenjärvi will face a similar situation next summer. Sojakka said lakes affected by blue-green algae usually experience blooms regularly each summer, but this is the first year Kolvosenjärvi has seen such an extensive phenomenon.

The Permit and Supervisory Agency, the City of Savonlinna and the Municipality of Enonkoski will soon organise a public information meeting for local residents.