The Daldykan River flows through the Siberian city of Norilsk, an industrial hub where temperatures have never gone above 0°C (32°F) during the winter months. Over the past week, the river has mysteriously changed from an icy blue color to a deep red.

Photos of the blood-red river swarmed across Russian social media site Vkontakte (VK). As of yet, no one’s quite sure what happened, although understandably many people are blaming a local industrial plant. This is not even the first time this seemingly biblical event has happened. A similar incident was reported back in 2014.

The river flows right alongside a metallurgical factory run by Norilsk Nickel, the world’s largest processor of nickel. A spokesperson from the factory told the Siberian Times that the situation is being investigated but they would not confirm a leak.

“As far as we know, the color of the river is today no different from normal,” added a company source. They then proceeded to send local news agencies with photos of the river looking a nice blue color.

The Guardian spoke to Denis Koshevoi, from the Vernadsky Institute of Geochemistry and Analytical Chemistry, who said that the Nadezhda factory uses pipes to pump metal concentrates and chemical solutions from nearby dams and mills. He also said that a pipe break and a leak could explain how the river changed color.

According to a statement from the Russian government, “a possible cause of pollution of the river could be a breakthrough slurry pipeline of the Norilsk Nickel factory."

It continued to say they will launch a formal investigation into the source of the contamination and evaluate the damage to the environment. 

^{A river bed from the surrounding area. © Liza Udilova/Greenpeace}