Alaska’s Rivers Turn Orange Due to Irreversible Permafrost Thaw Caused by Climate Change

The Salmon River in Alaska now runs a rusty orange thanks to metal contaminants unleashed by thawing permafrost. Credit: Taylor Rhoades

Several years ago scientists were alarmed by an environmental issue in the Brooks Mountain Range of Alaska. Rivers that had previously been clear and pristine began turning bright orange. This is a serious issue for fish and the ecosystems dependent on these waters. Researchers attributed this phenomenon to climate change and the associated increase in temperature. The associated thawing of permafrost,the stable, frozen ground found below the surface of even the tundra,deregulates the primary production in the watersheds found on the surface of the earth’s crust. During the thawing process, chemical reactions occur in the permafrost layer, which has, in some instances, released metals (e.g., iron, cadmium, and aluminum) into the rivers at low concentrations. According to Tim Lyons the lead scientist of the study, “This is not from mining…the permafrost is melting and changing the chemistry of the land.” The team invetigated the Salmon River, but the researchers warn there are similar transformations,i.e. metal pollution, fish die-off, across many Arctic watersheds.

When permafrost melts, then oxygen and water are now allowed to combine with sulfide-containing rocks to produce sulfuric acid. Once sulfuric acid is released and enters water systems it releases heavy metals into the rivers. Once metals are in the water, they can be detrimental to aquatic life as they also increase acidity of the water, decrease oxygen, and increase sediment which may inhibit fish spawning. At risk are key species such as salmon which are vital to Indigenous groups in the region.

David Cooper, one of the authors of the study, said, "The changes to water chemistry and the environment have been shocking to see". He first heard of the orange rivers in 2019 while conducting fieldwork when the pilot he was with said that the Salmon River remained orange, even after the snow melted.

While the levels of metals in the fish is not currently dangerous to humans, the impacts on the environment are severe. According to Lyons, "Once this starts, it doesn't stop. It's an irreversible effect of climate change".

Unlike a mine, these remote Arctic Rivers do not have any pollution controls, making it harder to stop the problem. The researchers hope that by reporting their findings will help to assist communities plan for these environmental challenges.

The research was funded through the U.S. National Science Foundation, and published in the Proceedings of the National Academy of Sciences, as an example of yet another way the effects of climate change are impacting the most remote areas on the planet.

References:

https://news.ucr.edu/articles/2025/09/08/orange-rivers-signal-toxic-shift-arctic-wilderness

https://www.pnas.org/doi/10.1073/pnas.2425644122#sec-2