Why some of Alaska's rivers are turning orange

Researchers for years have been baffled as rivers and streams across Alaska turned orange, but new research points to climate change as an answer.

Scientists suspect the drastic color change is the result of thawing permafrost — which essentially is frozen ground — releasing minerals into crystal clear water, according to a study published Monday in the journal Nature Earth and Environment. The change could threaten drinking water and fisheries in the area.

"Those orange streams can be problematic both in terms of being toxic but might also prevent migration of fish to spawning areas," lead author Jon O'Donnell, an ecologist for the National Park Service Arctic Inventory and Monitoring Network, said in a press release.

Here's a closer look at what's happening to Alaska's water.

Where are the orange streams and rivers?

The impacted water is in federal lands, including Gates of the Arctic and Kobuk Valley national parks, researchers said. Scientists sampled affected water across 75 locations in a Texas-sized area of northern Alaska's Brooks mountain range. Some of the sampled areas are so remote that helicopters are one of the only ways to access them.

"The more we flew around, we started noticing more and more orange rivers and streams," O'Donnell said. "There are certain sites that look almost like a milky orange juice."

A small headwater tributary of the Akillik Rivver in Kobuk Valley National Park in summer 2017 and summer 2018. / Credit: NPS / Jon O'Donnell

Some of the stained areas are so large that the orange rivers are visible from space, according to Brett Poulin, an assistant professor of environmental toxicology at UC Davis and a study researcher.

"These have to be stained a lot to pick them up from space," Poulin said in a press release.

O'Donnell first noticed a change in water in 2018, but researchers said satellite images recorded stained waters dating back to 2008.

"The issue is slowly propagating from small headwaters into bigger rivers over time," O'Donnell said. "When emergent issues or threats come about, we need to be able to understand them."

The National Park Service previously pointed to Salmon River as a particular point of concern. The water there was "pristine" before 2019. That summer, the clear water turned orange-green. The discoloration stuck around and there remain orange stains on the river banks.

What's in the orange water?

Scientists believe that minerals stored in permafrost were released as the climate warmed. The metal ores were exposed to water and oxygen, causing them to release acid and metals.

Samples showed elevated or high levels of iron, zinc, nickel, copper and cadmium in the impacted water. Iron is one of the most dominant metals and it is believed to be behind the orange coloration.

An orange tributary of Alaska's Kugororuk River / Credit: Josh Koch, U.S. Geological Survey

Some of the water samples had a pH of 2.3, compared to an average pH of 8 for rivers, which means the impacted water is significantly more acidic.

What are some future concerns?

Researchers are still working to understand what's happening with the colored water and what risks might exist for fishing stocks and drinking water. The study did note that "stream discoloration was associated with dramatic declines in macroinvertebrate diversity and fish abundance."

Alaska's Arctic rivers are home to a variety of fish that are "critical for subsistence, sport, and commercial fisheries," researchers wrote. Iron and other toxic metals in the water could threaten those fish.

Metals in the water could also impact rural drinking supplies. Researchers said that, at a minimum, they could impact the water's taste, requiring rural communities to enhance their water filtration.

"There's a lot of implications," O'Donnell said. "As the climate continues to warm, we would expect permafrost to continue to thaw and so wherever there are these types of minerals, there's potential for streams to be turning orange and becoming degraded in terms of water quality."

Researchers plan to study whether the rivers and streams can rebound if cold weather promotes permafrost recovery.