Cyanobacteria confirmed in lakewide bloom in eastern Finland

A bloom covering Kolvosenjärvi on the border of Savonlinna and Enonkoski in South Savo has been identified as cyanobacteria, Yle reports. The Finnish Environment Institute examined water samples from the lake.

The samples contained several types of cyanobacteria, all of which are capable of producing algal toxins. The bloom, first observed in July, is unusually extensive and covers the entire lake, which is estimated to be just over four kilometres long.

The bloom’s duration cannot be predicted, according to the Permit and Supervisory Agency, because it depends partly on weather conditions such as wind and temperature.

The agency said the cyanobacteria in Kolvosenjärvi behave unusually: they do not rise to the surface even when the lake water is left standing in a drinking glass.

The water must not be used for drinking, cooking, washing or sauna bathing. Swimming is also prohibited, as is using the water to irrigate plants intended for human consumption. The water is not suitable for animals to drink or for washing them.

The water may be used again only when it contains no algal particles or other signs of a bloom and has returned to its normal clear appearance, the agency said.

The Permit and Supervisory Agency detected the bloom in satellite images. Authorities also received reports from people in the area about the lake’s unusual condition. A worker from the City of Savonlinna collected water samples last Wednesday.

Similar blooms that cover entire lakes occur occasionally. Their formation is influenced by nutrient loading, weather conditions and characteristics of the lake, such as shallow water. Kolvosenjärvi has experienced blooms before, but only in its southern parts.