They called for the closure of a huge nickel mine in Sotkamo that last week leaked a cocktail of poisonous chemicals into surrounding rivers and lakes.
The Finnish Environment Institute tested water samples taken from the nearby Lumijoki river on Sunday and found high levels of aluminium, cadmium, nickel, uranium and zinc.
Banging drums and waving banners, people of all ages marched from the House of Parliament to the Ministry of Employment and the Economy and on to the Environment Ministry. There the marchers were met by Environment Minister Ville Niinistö and Labour Minister Lauri Ihalainen.
They handed Niinistö a petition calling for the mine to be shut down. The petition includes more than 17,000 names.
“If I wasn’t a government minister, I would have joined you,” said Niinistö, who is also the leader of the Green League.
Meanwhile in the northern city of Oulu, a few dozen protesters held an anti-Talvivaara demonstration on the central Rotuaari pedestrian street. They sang and lit candles to express sorrow at the pollution of waters around the mine.