Alaska’s Brooks Range rivers are turning rusty orange due to thawing permafrost releasing toxic metals into the water. This chemical reaction threatens fish, wildlife, and Indigenous communities who rely on these rivers for food and clean water.
A strange and concerning change is occurring in Alaska’s remote Brooks Range. The rivers that were once clear enough to drink have suddenly turned a murky, rusty orange. Scientists say that it could have serious consequences for fish, wildlife, and the people who depend on them.
As global temperatures rise, the Arctic is warming faster than almost anywhere else on Earth. One major effect of this is the thawing of permafrost, a layer of soil that normally stays frozen all year round. This frozen ground has locked away minerals and metals for thousands of years, but now it’s starting to melt.
When permafrost thaws, water and oxygen seep into the ground. This sets off a chemical reaction in rocks that contain sulphides. These reactions produce sulphuric acid, which then dissolves metals like iron, cadmium, and aluminium. These metals are washed into rivers, turning the water cloudy, orange, and sometimes toxic.
Normally, these kinds of chemical changes are linked to mining, where rocks are dug up and exposed to air and water. But in this case, there’s no mining activity nearby.
A Shocking Discovery
A new study published in the Proceedings of the National Academy of Sciences confirms the scale of the problem. The research focused on Alaska’s Salmon River, but scientists warn that many other Arctic rivers may already be going through the same changes.
David Cooper, one of the study’s authors from Colorado State University, says, “I have worked and travelled in the Brooks Range since 1976, and the recent changes in landforms and water chemistry are truly astounding.”
The scientists began studying the river to find out the cause behind this change. They discovered that melting permafrost was causing the breakdown of sulphide-rich rocks. As these rocks reacted with oxygen and water, they released acid and metals which can build up in fish and pose risks to animals like birds and bears that eat them.
In low levels, some metals aren’t especially harmful. But in the Salmon River, metal concentrations have now passed the safety limits set by the US Environmental Protection Agency.
Impact on Salmon and Local Communities
Experts say that the changes to the river could be devastating for fish species like chum salmon, which are an important food source for many Indigenous communities in Alaska. These salmon need clean, gravel riverbeds to lay their eggs, but the sediment and iron-rich water is clogging these beds and smothering insect larvae that salmon usually eat. Other fish species, such as grayling and Dolly Varden, might also struggle to survive in these changing conditions.
The levels of metal found in fish tissue don’t pose a direct danger to humans who eat them. However, the long-term effects on fish populations could affect the food security and traditional lifestyle of many Arctic communities.
One of the biggest concerns is that, unlike mining pollution, which can sometimes be managed with technology, this natural chemical process has no simple solution. In remote Arctic areas, these are no systems in place to stop or contain the spread of these metals.
The study, funded by the US National Science Foundation’s Rapid Response programme, is a clear signal that more areas could soon face similar problems. Scientists hope to bring awareness to help communities and environmentalists prepare for what’s coming.