Alaska’s Rivers Turn Orange as Melting Permafrost Releases Toxic Metals

In Alaska’s far north, rivers once known for their crystal-clear waters are turning an alarming shade of orange. Scientists say the culprit is climate change—thawing permafrost that is releasing a toxic cocktail of metals into the waterways.

Stretching more than a thousand kilometers across northern Alaska, the Brooks Mountain Range has long sustained Indigenous communities and supported migratory fish populations. 

But recent years have brought a disturbing transformation. Once pristine streams now resemble polluted mine runoff, threatening fish, wildlife, and the people who depend on them.

The phenomenon first caught the attention of Dr. Patrick Sullivan of the University of Alaska in 2019. 

“The river looked like a sewage channel,” Sullivan recalled in an interview with Al-Ain News. “That sight pushed me to investigate what was really happening beneath the surface.”

Sullivan led a team deep into Alaska’s wilderness to collect samples along the Salmon River. The expedition required small bush planes, long hikes through tundra, and inflatable rafts to navigate the river system. 

“It took about a week of intense fieldwork to gather samples across the watershed,” he said.

Their findings, published in Proceedings of the National Academy of Sciences on September 8, 2025, paint a troubling picture. Rising temperatures are thawing permafrost, exposing sulfide-rich rocks to oxidation. 

This process releases iron and other heavy metals—such as aluminum, copper, nickel, zinc, and cadmium—into the water.

“As the permafrost thaws, sulfide minerals like pyrite come into contact with oxygen and water,” Sullivan explained. 

“That triggers a geochemical reaction that produces acidic runoff and mobilizes toxic metals. The result is what we’re seeing now—rivers turning orange and murky.”

Tests showed elevated concentrations of these metals downstream from acidic seeps, with levels varying depending on the local geology. 

The contamination is already disrupting aquatic ecosystems and could be accumulating in the organs of fish, posing risks to larger wildlife such as birds and bears.

The World Meteorological Organization (WMO) reported that 2024 was the hottest year on record, with average temperatures 1.55°C above pre-industrial levels. 

That rise is accelerating the thaw of permafrost—long-frozen ground that once locked away sulfide minerals safely below the surface.

According to Sullivan, this process may continue for millennia. “It could stop if the permafrost recovers,” he said. “But if it doesn’t, these chemical reactions will go on until the newly exposed sulfide minerals have completely weathered. That could take thousands of years.”

Researchers have detected similar orange-stained rivers in northwestern Canada, the European Alps, Peru, and the highlands of Colorado, suggesting the phenomenon could become more widespread as global temperatures rise.

In Alaska, the consequences are already visible. The study found severe deterioration in salmon habitats, with shrinking fish populations affecting both the ecosystem and local communities that rely on the fish for food and income.

What was once the lifeblood of northern Alaska is now a warning sign for the planet—a vivid orange reminder of what happens when the frozen ground beneath our feet begins to melt.