>>7786101It's definitely not natural, and it's definitely not the Rio Tinto in Spain.
In this case it's mineral-laden waste from a former nickel and copper mine near Sudbury, Ontario (Canada).
The solid waste was being stored near the mine in special holding areas called impoundments, over time air and water oxidised the minerals in the waste which then leeched out of the storage area into the environment.
Here's another image from the same area taken as part of a series of photos that include the river image previously posted
>>7774120 