Streams in Alaska are turning orange with iron and sulfuric acid. Scientists are trying to figure out why
Dissolved oxygen was extremely low, and the pH was 6.4, about 100 times more acidic than the somewhat alkaline river into which the stream was flowing. The electrical conductivity, an indicator of dissolved metals or minerals, was closer to that of industrial wastewater than the average mountain stream. “Don’t drink this water,” Sullivan said.
More….
www.scientificamerican.com/article/why-are-alaskas-rivers-turning-orange/
Some researchers think acid from minerals is leaching iron from bedrock, and when those sediments hit running water and air, they oxidize and turn a rusty orange color.
www.newsweek.com/alaska-rivers-orange-why-1854543
Evidently, iron oxide bacteria is a thing.
en.m.wikipedia.org/wiki/Iron-oxidizing_bacteria
75 rivers in total
h/t SqueakyOne