For the past few years, several rivers in Alaska have turned a bright orange, visible from space. This unusual coloration is due to the release of toxic metals into the waterways, a phenomenon observed by researchers. They have identified at least 75 affected rivers and streams in the Brooks Range. Helicopter surveys have helped locate these discolored waterways.
Chemical analyses revealed high concentrations of zinc, nickel, copper, cadmium, and iron in these rivers. Iron is primarily responsible for the orange hue, while the high acidity levels, with pH as low as 2.3, are reminiscent of lemon juice or vinegar. These conditions are extremely toxic to aquatic life.
The toxic metals released by thawing permafrost turn Alaska's rivers bright orange and make them highly acidic. This section of the Kutuk River in Gates of the Arctic National Park looks like an orange paint spill from above.
Credit: Ken Hill/National Park Service The high concentration of metals and water acidity is linked to the thawing of permafrost, a permanently frozen layer of soil that covers vast areas of the Arctic. The release of these metals is caused by the thawing of this layer, exposing minerals that have been sealed for thousands of years. These minerals then dissolve into the water, contaminating the surrounding rivers and streams. Aquatic habitats undergo visual and chemical transformations, endangering local wildlife.
The acidification of the waters facilitates the dissolution of more metals, creating a worrying positive feedback loop. As temperatures rise, more permafrost melts, releasing even more toxic metals into the waterways. Researchers are particularly concerned about the harmful effects on fish, which could have major implications for U.S. fisheries.
Rivers that were once crystal clear are now bright orange. Here, a contaminated section of the Kutuk River runs alongside an unpolluted section of the same river.
Credit: Ken Hill/National Park Service
The idea for this study took shape in 2018 when researchers witnessed the transformation of a crystal-clear river into a rust-colored waterway within a year. Satellite images revealed orange rivers as early as 2008, confirming the extent of the phenomenon.
Researchers plan to continue their analyses this year to fully assess the scale of the problem. They fear that last year's record temperatures have accelerated the release of metals. The situation could worsen with ongoing climate change, leading to increased metal contamination of rivers.