Food Authority finds no likely disease behind mass fish deaths

The cause of the mass fish deaths at Lake Urpalonjärvi in Luumäki, South Karelia, remains unclear, Yle reports. The Finnish Food Authority says an infectious fish disease does not currently appear to be the likely cause.

About 7,000 kilograms of dead fish were removed from the lake last week after large numbers washed ashore. Tissue samples are being examined by the Food Authority for infectious fish diseases, with the final analysis expected to take four to six weeks.

Water samples have not revealed the cause of the deaths. The usual suspected causes, including oxygen depletion, have been ruled out. Oxygen levels in the lake showed no abnormalities.

One possible explanation is cyanobacteria. Anabaena cyanobacteria, which can produce neurotoxins under certain conditions, has been found along all of the lake’s shores. However, the quantities have not been unusually high, and biologist Roni Seppä said it is very rare for cyanobacteria to kill fish.

“The only cause I still suspect at this stage is cyanobacteria. Or something that has not been identified in testing,” Seppä said.

Dead fish have also sunk to the bottom of the lake. Seppä said they were unlikely to cause long-term harm because Urpalonjärvi is shallow and wind causes the water to circulate effectively.

Residents and holiday-home owners have been advised not to use the lake water or swim in it. The guidance is based on the cyanobacteria findings and the fact that the cause of the fish deaths has not yet been established.