Alaska Rivers Turn Orange: Permafrost Thaw Releases Toxic Metals
Thawing permafrost in Alaska is turning rivers orange by releasing toxic metals into once-pristine waterways
The writer John McPhee once described Alaska’s Salmon River as having “the clearest, purest water” he’d ever seen. Today, that same river runs orange with toxic metals unleashed by thawing permafrost.
“During the summer of 2019, the clear waters of the Salmon turned distinctly orange and have remained discolored and turbid since,” according to a new study published in the Proceedings of the National Academy of Sciences.
The Salmon River’s transformation represents a much larger crisis. In Alaska’s Brooks Range,75 streams have “recently turned orange and turbid,” the study found.
“This is what acid mine drainage looks like,” said Tim Lyons, a biogeochemist at the University of California, Riverside, and co-author of the study. “But here, there’s no mine. The permafrost is thawing and changing the chemistry of the landscape.”
The cause lies underground in permanently frozen soil, known as permafrost. As global temperatures rise, this ancient layer is thawing. When water and oxygen reach the newly exposed soil, they trigger chemical reactions that break down sulfide-rich rocks, creating sulfuric acid that leaches naturally occurring metals like iron, cadmium and aluminum from rocks into the river, the research shows.
Researchers tested 10 major tributaries of the Salmon River and found that nine had toxic concentrations of at least one metal on at least one of three sampling dates. The study shows that levels of metals in the river’s waters exceed U.S. Environmental Protection Agency (EPA) toxicity thresholds for aquatic life.
Metal levels in the Salmon River mainstem were dangerously high throughout most of its length, and exceeded EPA chronic exposure thresholds for total recoverable iron, total recoverable aluminum, and dissolved cadmium, all the way from its first major tributary to its mouth, the study found. At one location, aluminum concentrations reached nearly five times the safe limit for aquatic life.
Cadmium was present almost exclusively in dissolved form — something the study notes is “rare in aquatic ecosystems and highly toxic to aquatic organisms.” Pacific salmon (Oncorhynchus spp.) and Dolly Varden trout (Salvelinus malma) are among the most sensitive fish species to cadmium exposure, according to the research.
Metal fish and downstream contamination
These metals affect fish in multiple ways. Iron-clouded waters reduce the amount of light reaching the bottom of the river and smother insect larvae that salmon and other fish feed on. Aluminum and iron can accumulate in fish gills, limiting oxygen diffusion and potentially causing lethal respiratory distress, according to the study. The research notes that cadmium competes with calcium for binding sites on gill surfaces, leading to acute calcium deficiency and death.
While current metal concentrations in edible fish tissue aren’t considered hazardous to humans, the study notes that the changes pose indirect but serious threats to human health through the food system.
The problem extends beyond the Brooks Range mountains. Rivers contaminated by permafrost thaw flow hundreds of miles downstream to Kotzebue Sound, where the Kobuk River meets the Arctic Ocean, threatening salmon runs that support both commercial fishing and food for communities.
The study suggests that degraded spawning habitat in contaminated tributaries like the Salmon River might help explain “a recent crash in chum salmon returns, which local communities depend upon for commercial and subsistence harvest.”
According to the study, salmon returns to Kotzebue Sound provide important food for northwest Alaska residents, ranking third in importance behind caribou (Rangifer tarandus) and sheefish (Stenodus nelma).
The economic stakes are substantial. Between 1962 and 2023, the annual Kotzebue Sound commercial salmon harvest averaged 231,196 fish, according to the study. The record harvest of 695,153 fish in 2018 was valued at more than $2.25 million, the research shows.
According to the nonprofit American Rivers, the 380-mile (612-kilometer) Kobuk River starts in the Brooks Range. It flows west to the Arctic Ocean, supporting Indigenous Iñupiat communities with resources such as salmon and sheefish. Five Iñupiaq communities with about 1,800 people sit along the Kobuk River, along with numerous scattered family fishing and hunting camps.
China Kantner, who grew up on the Kobuk River and currently lives in Kotzebue, emphasizes how these watershed connections support communities across vast distances. “People of the Upper Kobuk are really feeding people from Point Hope to Palmer,” she said in an interview with the Northern Alaskan Environmental Center. “It really feeds the whole state.”
“I feel really connected to the land here,” Kantner added. “I can’t imagine it any other way. I’d be an entirely different person.”
The impacts are beginning to reach coastal villages like Kivalina, where residents depend on rivers that originate in the Brooks Range. Some tributaries of the Wulik River have already turned orange from permafrost thaw, raising concerns about what this contamination could mean for fish populations that coastal communities rely on.
“It would be a real big hurt on us,” Replogle Swan, president of the Kivalina Volunteer Search and Rescue, said to Scientific American about the potential impacts of rusting Wulik River tributaries to fish populations. “That fish is just a part of our lives.”
No end in sight
The problem extends far beyond Alaska’s borders. “It’s not just a Salmon River story,” Lyons said. “This is happening across the Arctic. Wherever you have the right kind of rock and thawing permafrost, this process can start.”
The rusty rivers highlight an “unforeseen consequence of climate change,” Brett Poulin, an environmental toxicologist from the University of California, Davis, who wasn’t involved in the study, told Mongabay. “Arctic environments are warming up to four times faster than the globe as a whole, and this is resulting in deterioration of water quality in the most pristine rivers in North America.”
“There’s no fixing this once it starts,” Lyons said. “It’s another irreversible shift driven by a warming planet.”
Unlike mine sites where acid drainage can be mitigated with containment systems, these remote watersheds might have hundreds of contamination sources and no such infrastructure, the study notes.
“There are few places left on Earth as untouched as these rivers,” Lyons said. “But even here, far from cities and highways, the fingerprint of global warming is unmistakable. No place is spared.”
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