Alaska's rivers are turning bright orange and as acidic as vinegar as toxic metal escapes from melting permafrost

Dozens of Alaskan rivers have turned bright orange in recent years because melting permafrost has released high levels of toxic metals into the waterways, a worrying new study reveals. The colorful contamination, which can be seen from space, is a potential ecological nightmare — and is likely to get even worse in the coming years, researchers say.

In the new study, which was published May 20 in the journal Communications Earth & Environment, researchers identified at least 75 orange rivers and streams in a Texas-size area of Alaska's Brooks mountain range. Most of the affected waterways were initially spotted by helicopter surveys of the area.

"The more we flew around, we started noticing more and more orange rivers and streams," study lead author Jon O'Donnell, an ecologist with the National Park Service's Arctic Inventory and Monitoring Network, said in a statement. "There are certain sites that look almost like a milky orange juice." 

Chemical analysis of the rusty rivers revealed high levels of zinc, nickel, copper and cadmium, as well as iron, which is largely responsible for the orange hue of the waterways. Researchers also found that the polluted waterways were unusually acidic: Some of the smaller streams had a pH of as low as 2.3, which is around the same as lemon juice or vinegar, according to the U.S. Geological Survey.  

The high metal concentration and acidity of the water can both be tied to melting permafrost — a permanently frozen layer of Earth's surface that covers large swaths of the Arctic. As the frozen ground thaws thanks to human-caused climate change, previously sealed minerals are exposed to rain for the first time in thousands of years, allowing metals to dissolve out of the rocks and into surrounding streams, which feed larger rivers.  

Not only are the affected habitats visually transformed but the high mineral concentrations are also highly toxic to most aquatic life. Researchers are particularly worried about what the toxic meltwater could be doing to spawning fish, which could have major knock-on effects on U.S. fisheries.

Related: US rivers are changing from blue to yellow and green, satellite images show