Thawing Permafrost Turns Alaska Rivers Orange and Toxic

Climate change is transforming waterways across remote Alaska, where thawing permafrost has caused more than 70 rivers and streams to develop an unusual orange color. Researchers from the United States Geological Survey (USGS), University of California (UC) Davis, and National Park Service traced the discoloration to minerals released from previously frozen soils, raising concerns about metal contamination in aquatic ecosystems.

The environmental changes first caught researchers' attention in 2018, when they returned to a small tributary they had studied the previous year. According to USGS research fish biologist Mike Carey, the water had changed dramatically and fish were no longer visible.

Scientists initially suspected an isolated incident. However, subsequent investigations identified more than 70 cases of similar discoloration across remote Alaska, prompting a broader investigation into the changing water chemistry.

A 2024 study published in Communications Earth & Environment linked the phenomenon to permafrost thaw. As previously frozen ground warms, water penetrates ancient soils and interacts with minerals that release metals, including iron, aluminum, manganese, zinc, nickel, cadmium, and rare earth elements.

Further research examined six Alaskan watersheds and found metal concentrations reaching 70 times normal levels at locations approximately 60 miles downstream. The findings appeared in AGU Advances and demonstrated that contamination could travel considerable distances through connected waterways.

Researchers described the process as acid rock drainage, in which oxidized minerals release sulfuric acid and metals. Although this phenomenon commonly occurs near mining operations, the affected Alaskan waterways are located far from known mining sites.

UC Davis senior author Brett Poulin said the main river channels retained their ability to regulate acidity despite increased metal concentrations.

"The good news is the river's mainstem did not become more acidic. It's buffering the pH, indicating there is some resiliency in this system," said Brett Poulin, senior author of the UC Davis study.

Poulin also highlighted the potential for metals to move beyond the locations where they initially enter waterways.

"But there are metals that increased downstream, and those can be transported very long distances."

Between 2022 and 2024, researchers spent the summer months collecting water samples from different watersheds to investigate the chemical changes. Their work examined how thawing ground and mineral oxidation affected water quality across the region.

Weather conditions also contributed to the process. Researchers identified unusually warm and wet conditions between 2018 and 2019 as important factors that intensified permafrost thaw and increased water movement through underground mineral deposits.

July 2019 remains Alaska's hottest month on record. The exceptionally warm summer was followed by a particularly snowy winter, creating conditions that encouraged further soil thaw and mineral interactions.

UC Davis Ph.D. student Taylor Evinger, lead author of the research paper, explained how snow cover can influence underground temperatures.

"When you have more snow, it insulates the soil, preventing refreezing," said Taylor Evinger, lead author of the study.

Evinger described how deeper water penetration may have triggered similar chemical changes across multiple watersheds.

"We think water went deeper into the soil because of soil thaw, interacted with these minerals, and all of these watersheds were triggered around the same time."

The phenomenon extends beyond Alaska, with similar changes reported in Canada and other boreal forests containing extensive permafrost. Despite elevated metal concentrations, Evinger said researchers have not observed widespread fish die-offs or water quality problems affecting local villages.