Nornickel has opened an investigation after suspending the employees responsible.
A Russian mining company has admitted an environmental incident at one of its Arctic Tundra plants.
Nornickel said it pumped industrial water into the adjacent territory "in order to prevent possible contingencies" at a tailings pond, thus committing "a gross violation of the rules".
The company said the water was "cleared" and there was "no threat of waste leakage".
But independent newspaper Novaya Gazeta has reported that the water was tainted with heavy metals coming from the tailings at the nearby nickel-processing plant of Talnakh.
Nornickel said it "suspended" the employees responsible for the violation.
It's the second time in less than two months that Nornickel, one of the world's largest nickel producers, has been connected to environmental incidents in the region.
In May, around 21,000 tons of diesel fuel leaked after a reservoir at a Nornickel-operated power plant collapsed, causing some of the fuel to gush into a lake that feeds into an arm of the Arctic Sea.
Both facilities involved in the incidents are near Norilsk, north of the Arctic Circle, 2,900 kilometres northeast of Moscow.