Alaska's once crystal-clear rivers now resemble dirty orange soda, puzzling researchers

• Researchers noticed that Alaskan streams had turned bright orange.
• Warmer summers and melting permafrost may be turning the water rusty and acidic.

“In a lifetime of descending rivers,” John McPhee wrote of Alaska’s Salmon River, “this was the clearest and the wildest river.”

The writer who toured the Salmon in 1975 might not recognize it today. Its clear waters have turned orange.

Located in the northwest of the state, the Salmon isn’t Alaska’s only orange river.

“At this point, we have over 75 streams that have been observed as orange,” Joshua Koch, a research hydrologist with the US Geological Survey, told Business Insider.

From the Chukchi Sea on Alaska’s west coast to the Beaufort Sea near the Canadian border, watercourses look like they’re rusting.

Seeing orange from the skies

Koch began monitoring Alaskan streams in 2015. In 2019, he first saw formerly translucent water turn orange.

He and his colleagues spoke with pilots and looked at satellite images and learned this wasn’t an isolated incident.

“It’s not the same everywhere,” he said, “but certainly we see that certain years — 2018 and 2019 — seemed to be sort of a trigger where after that period or during that period, a large number of streams started to be impacted by this orange discoloration.”

Now geologists, ecologists, and other scientists — from the US Geological Survey, the National Park Service, the University of California at Davis, Alaska Pacific University, and the University of Alaska in Anchorage — are all trying to figure out the rusty river mystery.

The melting permafrost

Even before researchers knew about the orange waters, they realized northern Alaska was rapidly changing.

“The Arctic is warming about four times faster than the rest of the planet,” Koch said.

Exactly what’s changing the streams isn’t simple to determine. It could be a number of factors, from warmer summers melting permafrost to erosion.

“A lot of the work is to try to gather all of these variables in order to come up with an explanation because there are lots of overlapping processes,” Koch said.

One hypothesis is that as the permafrost thaws, it allows water that once couldn’t get deep into the soil to run over rocks and transport minerals to the streams. Researchers now continuously monitor throughout the summer months to see how the mineral concentrations change, Koch said.

“We talk a lot about iron because it’s the visible change,” he said. “It’s bright orange.”

Satellite images can direct the scientists where to look next. When they find a newly orange stream and start testing, they usually learn it’s not just high in iron.

“We see other metals, including aluminum and manganese and zinc, are all elevated,” Koch said.

They often find sulfate in much higher concentrations than in clear streams. And the pH can be as low as 2, Koch said. It’s as if they’re flowing with lemon juice or vinegar.

Those acidic waters are terrible for the ecosystems.

When scientists went to the orange streams to count fish, insects, algae, and other aquatic life, “biodiversity just crashed,” biologist Mike Carey told Scientific American.

“The fish were totally gone,” Koch told BI.

The streams Koch monitors near the Brooks Range are fairly remote, but the rivers they feed into provide fish for human communities in this region. “That is definitely something that we are thinking about,” he said.

It’s still early in the project, which is why there’s so much uncertainty about the causes that are altering the streams, and how they might reverse it.

“Ideally, we’d like to come up with some ability to predict or get an idea of probability that different catchments will have this sort of change,” Koch said.