Dead fish have been spotted in the dozens after some 571,000 litres of untreated sewage leaked into the Vantaa river in Southern Finland on Friday. The leak occurred after a thunder storm cut power from vital flow control systems at Karoliinanoja in Riihimäki.
The sewage poured into the main channel of the 100-kilometre river and seeped into the Arolamminkoski rapids, at a water quality monitoring spot in Häme.
Kari Stenholm from the waterway maintenance society Virho says he personally saw at least ten dead fish floating in the water.
"There are definitely many, many more than that with the oxygen levels this low," Stenholm says. "It's so murky you can't even see all the dead fish."
On Saturday morning the oxygen content of the river water at Arolamminkoski was 0.5 mg/L – compared with the target content of about 8 mg/L.
The Riihimäki water power company says the sewage leak is not the only cause of the low oxygen levels, with dead fish reported on Thursday prior to the thunder storm.