Rusty rivers in Alaska. A climate tragedy in the wild north

Until recently, the 49th state of the USA was regarded as a symbol of pristine nature and a haven of unspoiled environment. Unfortunately, it may soon lose this honorable title. Rivers in Alaska are turning orange, and their waters contain dangerous concentrations of metals. The heaviest toll is paid by local fauna, but humans will also feel the consequences.

Virgin landscape stained with rust

The Brooks Range in Alaska is an area of exceptional ecological significance. This northernmost watershed in America separates streams flowing into the Arctic Ocean from those draining into the northern Pacific. It is a legendary refuge for many valuable fish species, as well as iconic mammals of the north: grizzly bears, Dall sheep, wolves, and moose. Hundreds of thousands of caribou migrate annually across the Brooks Range on their unique journey – the longest migration among all land animals.

Within the 14-million-hectare mountain range lies the wild and picturesque Salmon River watershed – one of the most remote and strictly protected in the entire United States. It was here, in the summer of 2019, that the shocking rusty coloration of previously crystal-clear water was first observed.

Rivers in Alaska are turning toxic

On September 8 this year, the journal PNAS published the results of the latest study on hydrological changes in Alaska. The authors focused on the Salmon River but emphasized that their observations and conclusions also apply to other watersheds in the region. David Cooper from Colorado State University speaks openly: I have worked and traveled in the Brooks Range since 1976, and the recent changes in the landscape and water chemistry are shocking.

The research shows that in the main channel of the Salmon River and in most of its tributaries, concentrations of iron, aluminum, and cadmium exceed the thresholds set by the U.S. Environmental Protection Agency (EPA) as the upper limit of toxicity for aquatic organisms. High concentrations of sulfate ions were also detected in the water, which, according to the study’s authors, indicates increased weathering of sulfide minerals.

Main cause: warmer climate, outlook: grim

A deeper analysis revealed that the rusty coloration of Alaskan rivers is the result of climate change – the Arctic is warming faster than any other region in the world. Higher temperatures cause permafrost to thaw, triggering a cascade of unfavorable geochemical reactions. As a result, rocks rich in sulfur compounds, such as pyrite, begin to oxidize and acidify aquatic environments, promoting the release of metals.

The orange water is not merely an aesthetic flaw ruining Alaska’s legendary landscapes. Over time, metals accumulate in fish and other aquatic organisms, causing toxic reactions. And that is not all. Harmful compounds move up the food chain as wild birds and mammals feed on fish to satisfy their hunger.

According to the study’s authors, the turbid, discolored waters of Alaskan rivers also hinder light penetration, which slows the development of insect larvae – an important food source for salmon and other predatory fish. The accumulating metallic sediments in riverbeds also appear to restrict the spawning of chum salmon – a species that is a dietary staple and a source of livelihood for local communities. Already a year ago, researchers from the National Park Service reported that in a small headwater stream of the Akillik River in Kobuk Valley National Park, they had recorded a sharp decline in the abundance and diversity of benthic invertebrates, along with a drastic drop in the number of juvenile Salvelinus malma, a common resident fish species.

Tim Lyons, a biochemist from the University of California, Riverside, warns that similar phenomena are already being observed throughout the Arctic. Wherever there are the right types of rocks and thawing permafrost, this process can begin, he adds.

Unfortunately, according to scientists, once permafrost starts to thaw and release metals into waterways, the phenomenon can no longer be stopped, and the changes will be irreversible. Halting the global rise in temperature thus seems to be Alaska’s only chance… If it is not already too late.

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main photo credit: Lisa Hupp, Alaska Region U.S. Fish & Wildlife Service/Flickr

Bibliography:

P.F. Sullivan,R.J. Dial,D.J. Cooper,C. Diamond,C.J. Tino,D.D. Gregory,R.E. Wong, & T.W. Lyons, Wild, scenic, and toxic: Recent degradation of an iconic Arctic watershed with permafrost thaw, Proc. Natl. Acad. Sci. U.S.A. 122 (37) e2425644122, https://doi.org/10.1073/pnas.2425644122 (2025).