Bird watchers found the dead fish on Tuesday about 300 meters towards the northern end of the lake.
A representative of Pirkanmaa Centre for Economic Development, Transport and the Environment (ELY Centre) visited the area on Tuesday and collected water and fish samples.
The fish samples were sent to the Finnish Food Safety Authority, Evira for examination while the result of the water sample is expected by the middle of next week.
The ELY Centre will investigate what caused the death of the fishes.
The removal of the carcass will be decided later. There are some settlements on the bank of the lake and there is a nauseating stench coming out of the rotten fishes.
The lake is a valuable water area for the birds.
