Footage has emerged of streams running orange near a disused copper-sulphide mine in Russia's Ural mountain range.
Drone footage uploaded by an Instagram travel blogger last week shows a landscape scarred by the apparent wastewater near the village of Lyovikha in western Siberia.
Russian prosecutors said they are inspecting a facility that is supposed to treat acid runoff from the abandoned mine, according to AFP.
"Since 2004, a copper pyrite mine has been abandoned there. It turned out to be flooded and now acidic rivers flow from there," the blogger, Sergey Zamkadniy, wrote on Instagram.
The waste was meant to be kept inside ponds and treated, but heavy rains have caused them to overflow.
After a local environmentalist reported the issue to authorities last year, he claimed he was told the company tasked with tackling the run-off had inadequate funds to buy enough lime to neutralise the acid.
A spokeswoman for local prosecutors said experts would take samples from the area to find out if treatment of the "acidic water" was in line with the rules.
The probe comes just weeks after the Kremlin was forced to announce a state of emergency in Siberia after a massive fuel leak left two rivers with a bloody red tinge.
Tens of thousands of tonnes of diesel is understood to have leaked from a local power plant, affecting more than 1000,000 sq metres of land in the region.
