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Permafrost Thaw Is Turning Alaska’s Salmon River Toxic, PNAS Study Finds

Field tests show dissolved and particulate metals exceed EPA aquatic toxicity thresholds.

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“This is what acid mine drainage looks like,” Tim Lyons, a biogeochemist at UC Riverside, told the university in a September 2025 article. “But here, there’s no mine.”
The scientists’ observations at the watershed suggest the potential for “for widespread future stream degradation with permafrost thaw further north and elsewhere at high latitudes,” they wrote. 

Overview

  • New peer-reviewed data from the Brooks Range confirm acidifying runoff from thawed permafrost is mobilizing iron, aluminum, cadmium and other metals into the Salmon River.
  • Researchers report cadmium accumulation in fish organs and warn of potential impacts on predators such as bears and birds that consume contaminated fish.
  • Nine of ten sampled tributaries exceeded EPA limits for at least one metal, while iron precipitates are reducing light and smothering benthic habitat.
  • Current metal levels in edible fish tissue are not deemed hazardous to humans, but salmon and key invertebrates face degraded spawning and feeding conditions.
  • The mine-like chemistry arises from oxidation of sulfide-rich rocks without any mine present, is appearing across dozens of Arctic watersheds, and offers few remedies beyond slowing permafrost thaw and expanding monitoring.