Satellite images from NASA’s Earth Observatory are showing that the Daldykan River, which recently turned blood red, has changed color before. Red discoloration has appeared in the river, which flows through the Siberian industrial city of Norilsk, multiple times this decade and in the 1990s.

Mining and metallurgical company Norilsk Nickel has said that heavy rains caused a filtration dam at its Nadezhda Metallurgical Plant to overflow. However, the Russian Ministry of Natural Resources is investigating whether a burst slurry pipeline actually caused the pollution, according to NASA.

The satellite images show similar staining in August 2016 and August 2001. In both years, red water can be seen for kilometers along a slurry pipeline carrying chemical waste away from the factory.

[H/T Gizmodo]

Stained red water near the Nadezhda Metallurgical Plant in Norilsk, Russia, in 2016. NASA Earth Observatory