A Russian mining giant admitted that a spill at one of its plants turned a river blood red last week.

Norilsk Nickel002 Archives the world's biggest producer of nickel and palladium, initially denied that its nickel processing factory had leaked industrial waste into the Daldykan river near the Arctic Circle.

The mining company said that, after an investigation, it found "abnormal heavy rain" on Sept. 5 had caused a tailings dam -- which holds mining residue and wastewater -- to overflow into the river.

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Norilsk Nickel said the area saw roughly 50 percent of its monthly average precipitation in rainfall over the course of 24 hours.

"The overflow of one of the dikes occurred, and water entered Daldykan river," Norilsk Nickel said in a Sept. 12 statement.

The company claimed the contamination was harmless and said it would work to avoid such incidents in the future.

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"Short-term river color staining with iron salts presents no hazards for people and river fauna," according to the statement.

Environmentalists and local indigenous residents reportedly disputed Norilsk Nickel's claim of no harm, no foul.

"You can't just say that it's no big deal. Right now there is a ministry of environment commission there," Alexei Kiselyov of Greenpeace Russia told AFP.

Kiselyov also told AFP that investigating pollution from Norilsk Nickel plants is complicated by the fact that the infrastructure sits in remote areas.

Mashable ImageAn ore mining and processing complex in Norilsk, Russia. Credit: Sovfoto/UIG via Getty Images

The mining giant also controls access to the entire Taymyr peninsula in the Russian Arctic.

The city of Norilsk, located in Russia's Krasnoyarsk Krai, is home to the world's largest heavy metals smelting complex and known to be one of the world's most polluted places.

More than 4 million tons of cadmium, copper, lead, nickel, arsenic, selenium and zinc are released into Norilsk's air every year.