A new study reports that rivers and streams in Alaska are changing color—from a clean, clear blue to a rusty orange—due to toxic metals released by thawing permafrost.

The finding surprised researchers from the National Park Service, the University of California at Davis, and the US Geological Survey, who conducted tests at 75 locations in the waterways of AlaskAlaska’sks Range. Over the past five to ten years, the rivers and streams in the range have rusted and become cloudy and orange, as reported in the study published in the journal Communications: Earth & Environment.

The discoloration and cloudiness are caused by metals such as iron, zinc, copper, nickel, and lead, which are toxic to river and stream ecosystems. These metals are released as permafrost thaws, exposing waterways to minerals locked underground for thousands of years.

“We’re”We’re to see this in parts of California and 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,” says” Brett Poulin, a co-author of the study and a professor of environmental toxicology at UC Davis. “But “it’s startling to see it when you’re some of the most remote wilderness, and you’re from a mined source.”

An “aerial view of the Kutuk River in AlaskAlaska’ss Arctic National Park shows orange paint-like discoloration spilling into the clear blue water. Arctic soils naturally contain organic carbon, nutrients, and metals, such as mercury, within their permafrost. As high temperatures cause permafrost to melt, these minerals and the surrounding water sources meet.

According to studies, the Arctic is warming four times faster than the rest of the world.

“What” we believe we’rewe’reng is this thawing of soil that’that’sening faster there than it would happen elsewhere,” said” Poulin. “It’s”It’s an unexpected consequence of climate change.”