Alaska rivers turn orange as permafrost thaw releases iron and metals

Satellite images from NASA and the USGS show that more than 200 rivers and streams in Alaska's Brooks Range have changed colour, appearing orange, yellow or rust‑red. The phenomenon is linked to the thawing of permafrost, which allows groundwater to reach iron‑rich sulphide rocks. Chemical reactions oxidise the iron and release sulphuric acid and other metals (zinc, nickel, copper, cadmium) into the water, creating a rust‑like coloration.

Analysis of Landsat archives indicates that most changes have occurred within the last decade, with a rapid shift evident around 2019‑2020. The discoloured waters display higher acidity, increased turbidity and elevated metal concentrations, leading to reduced diversity of aquatic invertebrates and lower fish populations. Researchers identify two mechanisms: oxidation of sulphide rocks in mountainous zones and microbially driven iron solubilisation in low‑lying wetland areas. The altered chemistry could affect isolated Alaskan communities that rely on these rivers for drinking water and subsistence fishing.