Why rivers and streams are turning orange in the US

Rivers and streams are changing colour in the United States.

The clear glacial blue of Alaska's waterways that people are accustomed to seeing is being tinged with a bright rusty orange.

Streaks of amber were found in 75 locations across the northern state, surprising researchers looking into the new phenomenon, according to a new study.

The discolouration is likely linked to climate change, specifically melting ice in the Arctic, experts say.

Here's exactly what is turning rivers orange, and why scientists are surprised by the findings.

What's in the water?

Rivers and streams in Alaska are changing colour because toxic metals are being released by melting permafrost, a study by researchers from the National Park Service, the University of California at Davis and the US Geological Survey found.

They tested 75 locations in the waterways of Alaska’s Brooks Range, which have become cloudy and orange over the past five to ten years, according to the study published in the journal Communications: Earth & Environment.

The discoloration and cloudiness is being caused by metals such as iron, zinc, copper, nickel and lead, the researchers found. Some of these are toxic to the river and its ecosystems.

Researchers used satellite imagery to determine when the change in colour happened in different rivers and streams.

Why are scientists shocked?

It is not abnormal for rivers near mines to turn orange but in the Arctic National Park, which is very remote, and miles from industrial or urban areas, this is a new phenomenon.

“We’re used to seeing this in parts of California, parts of Appalachia where we have mining history.

"This is a classic process that happens in rivers here in the continental US that have been impacted for over 100 years since some of the mining rushes in the 1850s,” said Brett Poulin, who was a co-author of the study, told ITV News partner CNN.

“But it’s very startling to see it when you’re on some of the most remote wilderness and you’re far from a mine source” the professor of environmental toxicology at the University of California said.

Previous studies have also found different types of thawing accelerated the discolouration of water.

One, published by Water Resources Research, discovered an increase in the same metals in 22 of Colorado’s mountain streams in the past 30 years.

Researchers attributed half of the increase in the newly orange water to minerals escaping the bedrock due to the thawing of frozen ground.

Similar results were also found after research in the Chilean Andes, the European Alps and the Pyrenees in northern Spain.

What's causing the orange to seep into the rivers?

Scientists say the orange-coloured leaks are linked to global warming.

All the toxic metals causing the discolouration have been stored underground for thousands of years, in the Arctic as permafrost.

But these minerals are leaking as the frost melts amid increasing temperatures. The rising water levels caused by the thaw mixes with the melting frost that contains the metals, causing the change in colour.

“What we believe we’re seeing is this thawing of soil that’s happening faster there than it would happen elsewhere,” said Mr Poulin. “It’s really an unexpected consequence of climate change.”

“At several of the locations it happened, the most drastic increases were between 2017 and 2018 and they coincided with the warmest years on record at that point,” said Poulin.

Is the orange causing problems?

Some of the minerals which have leaked into the rivers are toxic, and in some cases linked to “dramatic declines” in aquatic life.

The study recorded some samples of water had a pH of 2.3 compared to the average pH of 8.

This means the sulfide minerals are resulting in highly acidic and corrosive conditions.

It is leading to concerns that if the melting continues, it could affect communities that rely on waterways for drinking and fishing.

Mr Poulin told CNN the communities living by the waterways had voiced their concerns and observations to study researchers beginning seven years ago.

Researchers in Alaska will continue their study in the coming years to determine the location of the metal and mineral sources, and how those who rely on the rivers will be impacted.

Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know...