In Alaska’s Brooks Range, a wilderness of rugged peaks and crystalline rivers just north of the Arctic Circle, a strange new force is blighting the landscape.
Bright orange water is flowing through rivers in quantities visible from outer space. As with wastewater from mines, the rust-orange colour comes from iron that dissolves after exposure to acidic water. But in this case, mining isn’t the culprit, it’s global warming.
“I’ve been most startled by the spatial extent,” says Brett Poulin, a scientist at the University of California, Davis who studies “rusting” rivers. “And there’s no way to stop it,” he adds. “Once it starts, it just starts.”
The phenomenon has been observed across the far-flung corners of the Arctic. In northwestern Canada, researchers have found rivers with the same orange colouring. Satellite imagery analysed by the FT and confirmed by experts at the University of Alaska and the Alfred Wegener Institute — a German research centre that regularly collaborated with researchers in Russia until the Ukraine war — has also revealed probable rusting rivers in Siberia.
In the Brooks Range alone, scientists working with bush pilots, park rangers and other locals highlighted more than 200 rusting waterways last year.
Iron is not the only metal washing through. Manganese and nickel levels are rising in some of the affected rivers. Dissolved aluminium is also turning rivers white outside of the Arctic in the European Alps and the Pyrenees mountains.
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Beyond the local impact of metal-laden rivers, the phenomenon is a harbinger of a much larger and troubling problem. In many of the affected rivers, scientists have identified thawing permafrost as a key factor.
Permafrost, or ground that is frozen for at least two consecutive years, can contain organic materials and minerals. When permafrost thaws, it can set off a chemical reaction that causes metals to leach into water systems.
Thawing permafrost can also gradually but continuously release greenhouse gases such as carbon and methane into the atmosphere as microbes — otherwise dormant in the frozen ground — break down organic material, says Christina Schaedel, senior research scientist at the Woodwell Climate Research Center in Massachusetts.
The Arctic Institute, a non-profit organisation based in Washington, estimates the world’s reserves of permafrost contain up to 1.7tn tonnes of carbon, or about 45 times the emissions from all countries in 2024.
By 2100, near-surface permafrost, or the upper 3 to 4 metres of frozen ground, will be nearly gone, scientists estimate. The release of carbon from permafrost is expected to worsen global warming — and with it, wildfires, flooding and land collapse in polar regions — which in turn will cause more of the frozen earth to thaw.
“It’s not dwarfing our human emissions,” Schaedel emphasises. But it is a process that will continue even if warming slows: “We’re committing future generations to additional carbon loss from permafrost.”
In the Arctic, the past 10 years have been the warmest decade on record, with 2025 hitting a record low in winter sea ice in the 47-year satellite record, according to an annual report by the US National Oceanic and Atmospheric Administration last year.
Currently, the world is on track to hit 1.5C of global warming above pre-industrial levels by 2030, a decade earlier than previously thought, according to the EU’s Earth observation service Copernicus in January, as emissions stemming from burning of fossil fuels continue to rise.
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If that key threshold is crossed, scientists believe irreversible changes to the planet will kick in, endangering economic growth, water supplies and human health. The metal-laced rivers are an example of what scientists warn will occur across Earth’s systems.
“If people say climate change is a hoax, then send them to Abisko, then they can actually follow it with their own eyes,” says Andreas Kappler from the University of Tübingen, referring to a tiny Swedish village where he has studied permafrost.
Pointing to research published in the late 2000s, Kappler said at that time there were researchers who thought permafrost in Abisko, which sits above the Arctic Circle, would last until 2050. “Now they estimate maybe 2030, 2035.”
“It’s too late to reverse this,” he adds. “This permafrost region will disappear. I think this is very, very clear.”
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The phenomenon of rusting rivers is not always driven by climate change; mining can cause metals to leach into water. In other places, dissolved metals have flowed for so long that the phenomenon is reflected in the river’s name, such as Canada’s Arctic Red River or Tsiigehnjik in the indigenous Gwich’in language, which means “iron river.”
But as temperatures rise, especially in the Arctic — which is warming more than two times faster than the global average — the chemical reaction behind rust-coloured rivers is occurring in new places.
Thawed permafrost and melting glaciers can expose previously inaccessible minerals to water and oxidants, such as oxygen. If sulphide minerals, namely pyrite — the most common one — are present, a chemical reaction creates sulphuric acid, which then changes the pH of the water. More acidic water dissolves metals from the minerals.
Microbes once warmed and reactivated may further accelerate this process, known as acid rock drainage.
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Joel Hibbard, who runs the touring company Nahanni River Adventures & Canadian River Expeditions, first came across rusty water when hiking in Canada’s Northwest Territories in 2016. He had stopped at a familiar spot for hydrating, but that day the typically clear water was orange. “It had a really metallic taste to it,” Hibbard says.
Since then, staff have encountered more rust-coloured rivers and Hibbard has stopped taking tourists to affected areas until the company knows more. A team of Canadian researchers has flagged to Hibbard the high and potentially unsafe levels of manganese and cadmium in some rivers.
“I don’t know what will happen,” says Hibbard, who worries about the impact the water could have on local wildlife, communities and his business if it persists. “We’ve always prided ourselves on a leave-no-trace ethos — and now it’s the land that is pushing us away.”
In Switzerland, Christoph Wanner from the University of Bern first became aware of white-tinted rivers resulting from acid rock drainage more than 15 years ago. At the time, a local hunter had tipped off his student, who then brought a whitened rock from the mountains back to the university.
Iron requires more acidic water to dissolve, whereas aluminium, the metal creating chalky-white residue in rivers in the European Alps, dissolves in less acidic conditions, Wanner explains. “The rock has to be right. It doesn’t happen in all the geological formations,” he says.
Local conditions, such as water flow and geology, also determine the severity and duration of metal seepage into waterways. Rivers that initially run bright orange may become more diluted over time, while others may deepen in colour.
On the Wildspitze, the second highest mountain in Austria, levels of nickel have surpassed water quality limits in some areas as temperatures rise.
“Acid rock drainage in our working area was quite a surprise for me,” says Peter Rose, managing director at Hydroisotop GmbH, a company that operates an environmental laboratory. In 2024, the lab installed water filters at one mountain refuge, which involved hiking up the terrain with large metal tanks.
At one spot, the concentration of nickel in the water had nearly doubled from 64 micrograms per litre to 110 between August 2023 and 2025, says Rose. The maximum level of nickel allowed in natural mineral drinking water according to EU rules is 20 micrograms per litre. The drinking water for the hostels comes from nearby glaciers, explains Rose, which are “melting at a progressing rate, quicker and quicker”.
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In the Alps, changes due to permafrost thaw have been particularly striking, adds Wanner. In an area in northern Italy he studied in 2003, it was rare to find river rocks that had turned white due to dissolved aluminium. By 2021, the amount of white residue in the same place was “huge”, he says.
Thawing permafrost and glacial melt are also contributing to rock slides and the destabilisation of rock glaciers, says Wanner, which not only threaten hikers and climbers, but also alpine communities. In May 2025, a landslide triggered by the collapse of a glacier in southern Switzerland buried the village of Blatten, days after its residents had been evacuated.
Further south on the border of France and Spain, white residue is even spreading to the “pristine environments of the Pyrenees headwaters”, says Mario Zarroca, a scientist at the Universitat Autònoma de Barcelona who began observing white rivers in the mountain range in 2012.
Unlike in Alaska or Canada, the dissolution of metals in the Pyrenees does not necessarily come from thawing permafrost, but intensifying drought and rising temperatures, explains Zarroca.
Once triggered, increases in temperature intensify the process by accelerating the rate of pyrite oxidation, he says. Microbes that oxidise minerals also prefer working in warmer conditions.
“The phenomenon, far from ceasing, seems to be becoming increasingly active and expanding to many more places,” he says, adding that levels of nickel and arsenic from some springs are well above drinking water standards.
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The elevated concentration of metals in water may not pose an immediate risk to humans, but can be harmful if consumed in large quantities, scientists say.
In Svalbard, a Norwegian archipelago just south of the North Pole, the level of the mineral manganese shot up from less than 100 micrograms per litre in July 2024 to over 600 in early 2025, after a temporary increase in late 2023. Members of Longyearbyen council had to reassure residents that the manganese posed “no risk of acute poisoning”, only “potential effects from long-term intake”.
“Manganese is an essential element, which we all need but not too much,” says Gijsbert Breedveld, a professor at the University Centre in Svalbard, who gave a presentation on the risks of manganese at a Longyearbyen town meeting last month.
The local brewery now provides free filtered water for residents, according to an official announcement in September, which also advised locals against drinking tap water. Some sites such as local kindergartens and the university have installed filters for the drinking water supply.
Breedveld says the retreat of glaciers is one factor behind the heightened manganese levels. “Sediments are becoming available and release minerals,” he says, adding that it isn’t clear how much of a role climate change plays compared to other important factors, like the presence of mines near Longyearbyen.
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Far from the archipelago’s coal mines, however, rust-orange water is flowing in other, albeit uninhabited, parts of Svalbard, says Andy Hodson from the University Centre in Svalbard. Increased rainfall is a likely factor, he says, rather than snow.
The upper layer of permafrost that thaws during the summer has also been “deepening every year due to ongoing climate warming”, leading to new interactions between pyrite, water, metals and microbes, says Hodson.
In Alaska, changes to water chemistry are already affecting communities that rely on local fish as part of their diet. In the Brooks Range, populations of Arctic grayling, a freshwater fish, have disappeared from rust-orange rivers.
“People here are very attuned to the environment,” says Jack Reakoff, who has lived in the Brooks Range for more than 60 years. He and his wife lead a subsistence lifestyle, relying on hunting, trapping, fishing and a vegetable garden for food.
In 2017, Reakoff saw water the colour of “orange juice” gush through a local creek. Since then, the 68-year-old has encountered many more rust-coloured waterways, which may be too acidic for the Arctic grayling, he says.
In a 2024 paper, National Park Service staff and partnering scientists observed declines in both Dolly Varden trout and other small aquatic species after “rusting” occurred.
For Reakoff, rusting rivers are just another “facet of climate change” that is making it more difficult for locals to survive off the land. Over the past decade, warming temperatures along with over-hunting have shrunk local caribou, moose, sheep and salmon populations, he says.
“We have to work harder to come up with the amount of food that we need to live here,” says Reakoff, who adds that last year was the first time he was unable to hunt down a moose since 1991. “I worked harder, I spent more time out every day.
“The outlook is bleak,” he says.
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As the planet warms, the Arctic itself is becoming a source of greenhouse gases.
In addition to permafrost thaw, wildfires, which release carbon, are increasing in frequency. In 2024, the combination of wildfires and permafrost thaw in the Arctic tundra meant that, for the first time in millennia, the region emitted more carbon than it stored, according to Noaa.
However, projections of emissions scenarios and climate models often underestimate how much carbon will be released by thawing permafrost, say researchers. This is partly because the Arctic is so remote and vast, which makes data coverage and field work — including the work of identifying rusting rivers — both challenging and expensive.
Most field work is also restricted to warmer months in polar regions, further limiting access. And despite being grouped together as the Arctic, the region contains diverse landscapes that may each experience different effects from climate change in the future.
In addition, almost half of the Arctic’s permafrost is in Russia. The lack of institutional exchange with the country’s universities because it is isolated by western powers is another “real challenge”, according to Guido Grosse, head of permafrost research at the Alfred Wegener Institute. The lack of data from ground stations and an over-reliance on remote sensing risk distorting scientific understanding of Arctic change, warn scholars.
“If we’re talking about any policy action that keeps us within certain temperature goals, if we’re not fully accounting for all the emissions, we are [working towards] a wrong target,” says Schaedel.
The speed of warming is such that Arctic researchers increasingly wonder when permafrost will disappear from the places they study, something that once felt distant and abstract. Sebastian Westermann from the University of Oslo says this could be the reality within 20 years in field sites in northern Norway.
“That’s actually quite something — that you plan for the end of your field measurements because permafrost is gone,” he says.
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