Hundreds of Arctic rivers and streams are turning bright red-orange, not from chemical pollution, but from naturally occurring iron spilling from long-frozen ground as temperatures warm. The "rusting rivers" phenomenon, which has been documented across the Brooks Range in northern Alaska, offers a vivid example of the effects of climate change in a region that is warming faster than the global average.
The finding was reported in the National Oceanic and Atmospheric Administration's annual Arctic Report Card, released Tuesday. NOAA has released the report for 20 years as a way to track rapid changes in the northernmost part of the planet.
Those decades have seen rapid environmental change in the region. The most recent year was the warmest and wettest in the Arctic's recorded history, said Matthew Druckenmiller, a senior scientist at the National Snow and Ice Data Center, in Boulder, Colorado, and lead editor of this year's report card. He said Arctic warming influences global sea-level rise, weather patterns, and commercial fisheries.
The Arctic "is really the refrigerator for the planet," said Druckenmiller. "When the Arctic thaws and warms, it's having an impact on the global climate."
This year's report comes amid sweeping changes to federal science and climate research. President Trump refers to climate change as a "hoax," and his administration has curtailed climate science by cutting research budgets at universities and federal agencies, firing federal scientists, and stopping work on the National Climate Assessment.
"Pretty much everything having to do with climate change — the climate crisis — has undergone huge cuts," said Jennifer Francis, a scientist at the Woodwell Climate Research Center in Falmouth, Massachusetts, who was not involved with this year's Arctic Report Card.
An independent network of global scientists writes and compiles the research in the annual report, offering it some shelter from political winds. Some sections of this year's edition openly discuss the effects of climate change, and at least one study notes its major cause—burning fossil fuels.
"The U.S. administration's perspective on climate research is shifting, and certainly that brings concerns around being able to work on a report like this," said Druckenmiller. "But in the end we had full support from NOAA."
The report "highlights the critical value of sustained, collaborative observations for understanding and responding to rapid Arctic change," said acting NOAA Chief Scientist Steve Thur, in a statement. "NOAA remains committed to meeting this challenge."
Here are some highlights from this year's report: Josh Koch, a research hydrologist for the U.S. Geological Survey, said people started noticing the bright-orange "rusting rivers" around 2018.
" We heard from people who live in the region—pilots who are often flying over, people in the national parks," said Koch, whose research is featured in this year's report card. Over ensuing years, satellite imagery, water testing and ground observations revealed contaminated rivers over hundreds of miles in remote parts of Alaska.
Koch said that the thawing of long-frozen ground known as permafrost is likely triggering the discoloration. As water and oxygen infiltrate melting soil, naturally occurring iron and other metals seep into nearby streams.
"It's often not orange until it reaches the stream, and then all the iron and other metals can precipitate and create this iron staining," said Koch. He said the changes can happen over a matter of days or weeks.
Other metals, such as copper and aluminum, are also being released from thawing permafrost. Those metals could harm fish, which could then impact other animals in the food chain. Scientists are studying whether the metals could contaminate rural drinking water supplies, said Koch, but haven't seen any impacts yet.
Shrinking glaciers, rising seas
The Greenland Ice Sheet lost 129 billion tons of ice in 2025, continuing its long-term trend. Arctic glaciers outside Greenland have also rapidly thinned since the 1950s; Alaskan glaciers have lost an average of 125 vertical feet since that time.
The thinning and melting glaciers cause immediate and longer-term danger, said Druckenmiller. The melting of the Mendenhall Glacier near Juneau, Alaska, for instance, led to sudden glacial outbursts of water in recent years, causing devastating floods.
Globally, ongoing glacier loss contributes to steadily rising global sea levels, which increase danger from flooding, erosion and storm surge in coastal communities.
Warmer, saltier water is showing up in the Arctic Ocean near the North Pole. There's a word for this — Atlantification — and it's contributing to record low sea ice in the region. This year saw the lowest sea-ice extent in the 47-year satellite record.
Similar warming is happening in the Bering Sea, which is home to Alaska Pollock, Pacific Salmon and other important commercial fish species. There, warming waters are leading to an increase in southern species of marine life and a decrease in Arctic species. Druckenmiller said the changes are disrupting both traditional hunting practices and commercial fisheries. "The food chain is connected to the lives of people living in the Arctic," he said.
