Alaska's Rivers Are Turning Orange, and the Ground Itself Is to Blame

Hundreds of crystal-clear rivers and streams in Alaska's Brooks Range have turned the color of old pennies, and the culprit isn't a spill or a mine. It's the ground thawing out.

Satellite, aerial and ground-based surveys spanning more than 600 miles (966 kilometers) across the Brooks Range have documented color changes in more than 200 watersheds, with most shifts occurring within the past 10 to 12 years, coinciding with rising air and ground temperatures. Thawing permafrost is the most likely cause.

Here's the mechanism, because it's actually wild: permafrost acts as a deep freeze for minerals in the soil, including iron sulfides and other metals that, when locked in ice, stay chemically inert. Once that ice thaws and oxygen and water reach those minerals for what may be the first time in thousands of years, the metals oxidize. The iron turns to iron oxide. Rust. Researchers have described the phenomenon as an unforeseen consequence of permafrost thaw across the Arctic, a chemical cascade that nobody anticipated when warming began. The streams didn't import the rust from somewhere else. They're making it themselves, from the inside out.

The affected waterways now number in the hundreds, including streams inside designated National Wild and Scenic River corridors, with some appearing to shift almost overnight. NASA/USGS Landsat satellite data helped establish the timing of several of those changes. Ground and aerial surveys along one affected waterway, the Agashashok River, found an orange section several kilometers long, with vegetation near groundwater seeps and springs appearing blackened.

What scientists still don't fully understand is what triggers the shift in any particular stream, or how the process unfolds season to season. Heavy winter snowpack is one suspected factor, keeping ground temperatures warmer than usual through winter and accelerating permafrost breakdown the following summer.

The permafrost was the lid. It's coming off.

Read the full story at NASA Earth Observatory, July 14, 2026

Hot Take: There is something genuinely arresting about iron that has been locked in frozen ground since before human civilization just... waking up. The permafrost isn't a passive bystander in all this; it turns out it was an entire geochemical system on pause, and we are now watching it hit play. Every geology teacher has a speech about how the planet is always doing something enormous that we're too small and too impatient to notice. This one we're finally noticing, and the river is orange.