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The Rusting Rivers · The Climate Translation

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In my research travels, I've spent time in Alaska and witnessed the beauty of the land
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there.
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The mountains rise above the ground, forest and grasslands stretched to the skyline and
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rivers cut through the landscape.
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But what would you think if you were hiking there and came across a river that was orange
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with rocks along the bottom coated with something that looked like rust?
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Your first thought might be that there's a mine upstream, or maybe an industrial spill.
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But what you're witnessing isn't man-made pollution, instead it's coming from the ground
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itself.
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Today, we're going to talk about how climate change can alter something most of us would
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never think about, the chemistry of a river.
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Welcome back to the podcast, I'm Dr. Mac, and this is the Climate Translation.
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So what exactly is turning these rivers orange?
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The short answer is iron, or more specifically, the formation of rust.
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To understand how it gets into the water, we need to go underground.
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As much of Arctic Alaska, the ground remains frozen year after year.
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We call it permafrost.
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We've talked about it on the podcast before, particularly because frozen ground can store
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enormous amounts of carbon.
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But permafrost freezes more than soil and organic material.
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It also affects how water moves underground.
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Imagine a layer of permanently frozen ground beneath the surface.
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Rain and melting snow can soak into the upper soil during the summer, but that frozen
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layer acts like a barrier.
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Water can't easily travel deeper into the ground.
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But as the Arctic warms, that changes.
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The layer that thaws each summer can become deeper, in some places sections of the ground
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that were once frozen year round, remain thawed.
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Suddenly, water can reach rocks and minerals that it rarely interacted with before.
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And some of those rocks contain a mineral called pyrite.
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You may know pyrite by another name, Fools Gold.
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Pyrite contains iron and sulfur.
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And when it remains buried and isolated from water and oxygen, not much happens.
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But exposed it to both, and chemistry takes over.
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The pyrite begins to break down, and iron is released.
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Sulfur reacts with the water and oxygen to produce sulfuric acid, and that acidic water
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can dissolve additional metals from the surrounding rock.
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Scientists call this process acid rock drainage.
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If that sounds like a familiar process, there's a reason.
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The same basic chemistry can occur around mines when digging exposes sulfide-rich rock
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to air and water.
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But in these remote, Alaskan watersheds, nobody's digging mines.
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Thawing permafrost is providing the access.
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Groundwater moves through the newly thawed rock, picking up iron and sulfate and acid and
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other dissolved metals, and eventually emerges from the hillsides in small springs and
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seaps.
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That water then flows into nearby streams, and once the dissolved iron reaches the oxygen-rich
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water at the surface, it reacts again.
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The iron oxidizes.
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In other words, it rusts.
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Tiny iron-rich particles form in the water and then settle into the streambed, coating
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rocks with orange material, scientists are seeing across, for instance, the Brooks Range.
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It's very similar to what happens when you leave a piece of iron outside in the rain.
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The only difference here is the scale.
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Instead of rust forming on a nail or an old piece of metal, the chemical reaction is
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occurring across an entire watershed.
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And that orange color is really only the part that we can see.
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The same process can release metals such as zinc and nickel, copper, aluminum, manganese
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and cadmium.
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Some of these can become a bigger problem for aquatic life than the iron itself.
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So when scientists see a river turn orange, they're not just simply looking at a strange
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change in color.
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They're seeing evidence that the chemistry beneath the landscape has changed.
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And new research is showing that once those chemicals enter a river, they may travel
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much farther downstream than anyone initially expected.
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At first glance, this might seem like a very local problem, a small spring emerges from
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thawing ground, the water picks up iron in other metals, and a nearby creek turns orange.
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But then perhaps a few miles downstream, everything returns to normal.
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But new research suggests that the chemistry travels much farther than that.
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In September of 2026, a team led by Taylor Evinger and Jonathan O'Donnell with the US Geological
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Survey and several partner institutions published a study in the AGU Advances Journal examining
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six watersheds across Alaska's Brooks Range.
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The researchers collected water samples from places where acidic groundwater entered streams
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from affected tributaries and from larger rivers farther downstream.
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And the differences were striking.
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Some of the small seeps coming directly out of the ground were extremely acidic.
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They also contained much higher concentrations of sulfate and metals such as iron, aluminum,
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manganese, zinc, nickel, and cadmium than the nearby unaffected water.
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But then those streams flowed into larger rivers.
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He might expect some of the chemistry to be diluted and disappear, and some of it did,
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but not all of it.
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In the Salmon River watershed, researchers could still detect elevated levels of several
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metals more than 100 kilometers or 60 miles downstream from where the acidic water first
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entered the river system.
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In some cases, concentrations remained as much as 70 times higher than they had been upstream
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of the affected area.
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And that's important because the river did not necessarily look dramatically polluted
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that far downstream.
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The bright orange iron that we can see with our eyes is only one part of the story.
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Some metals remained dissolved in the water, others attach themselves to tiny particles
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and sediment, and both can continue moving down with the river.
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There was another interesting finding.
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Even though some of the small tributaries and seeps were extremely acidic, the larger
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rivers often did not become strongly acidic themselves.
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And the reason is because of buffering.
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Think about adding lemon juice to a large glass of water, and then also doing it to a teaspoon
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of water.
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The larger volume can absorb more of the acid without changing it dramatically.
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Rivers can do something similar, chemically.
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Certain minerals dissolved in water can neutralize some of the incoming acid, so the main river
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may maintain a fairly normal pH, even while carrying much higher concentrations of sulfate
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and metals.
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That means simply measuring acidity won't tell you the whole story.
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The researchers also found evidence that some of the changes happened remarkably quickly.
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Water quality records from two watersheds showed major jumps in sulfate and zinc beginning
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around 2019 and 2020.
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Those changes followed an unusually warm and then snowy winter.
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And once the chemistry shifted, it persisted for several years.
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So what looked like a slow process with permafrost gradually thawing over decades could produce
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a much more sudden change in a river.
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One year the water chemistry may look relatively normal, and then a few years later an entire
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stretch of the watershed may be carrying metals that were previously locked underground.
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And once those metals begin moving downstream, the next question becomes unavoidable.
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What happens to the organisms that live in the water?
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Once the chemistry of a river changes, the organisms living in it have to respond.
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And in Arctic Alaska, one of the fish scientists are closely watching is the Dolly Varden.
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Dolly Varden are members of the salmon family, and like salmon they spend most of their
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lives in the ocean and then return to fresh water streams to spawn.
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That makes clean, cold river habitats extremely important.
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But rusting rivers can change that habitat in several ways at once.
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The most obvious problem is the metals.
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Some metals, including zinc, copper, aluminum, and cadmium, can become toxic to fish when
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concentrations become high enough.
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And acidity can make the problem worse.
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As water becomes more acidic, some metals become easier for aquatic organisms to absorb.
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But toxicity is only part of the story.
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Remember the orange coating we talked about earlier?
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That iron can settle into the stream bed.
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And for fish trying to reproduce, the stream bed is important.
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Dolly Varden lay their eggs in gravel.
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Water normally moves through the spaces between those rocks carrying oxygen to the developing
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eggs.
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But if iron-rich material begins coating and clogging those spaces, water can't circulate
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as easily, and that could reduce the oxygen reaching the eggs.
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The chemistry can also affect the smaller organisms living on the bottom of the river.
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Aquatic insects and other tiny animals make up an important part of the food web for
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fish.
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The United States Geological Survey researchers have already found that orange streams tend
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to have a poorer habitat for these bottom dwelling organisms than nearby clear streams.
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So a river can change in several ways at once.
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The water chemistry can change.
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The stream bed can change.
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The food supply can change.
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And many fish avoid sections of water altogether if the conditions become stressful enough.
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In September of 2026, researchers published a study specifically looking at how much
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known Dolly Varden spawning habitat overlaps with these rusting rivers.
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They used decades of satellite imagery to track where streams had changed color, and then
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compare those locations with mapped spawning areas across Northwest Alaska.
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And the results were highly variable.
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Some rivers showed little or no overlap.
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Others showed much more.
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Across the entire region, the percentage of known spawning habitat affected in any given
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year ranged from 0 to 21%.
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In individual watersheds, the overlap was sometimes much greater.
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In the Wulik River, more than half of the mapped spawning habitats were affected
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during one year.
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In smaller streams, researchers found years when all of the mapped spawning habitat
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overlap with the degraded water.
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Now, it doesn't mean that all of the fish disappeared.
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And the researchers were careful to make that claim.
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The study measured the overlap between the degraded water and the spawning habitat.
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It did not measure how many fish survived or how many eggs successfully hatched.
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But it tells scientists where the risk may be the greatest.
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And that's important because these rivers are not just ecosystems.
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They also support fish that are important to local communities for substance and recreation.
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So the orange color may be the first thing people notice, but the deeper concern is what
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the color represents.
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The chemical change beginning underground can move into a stream, travel downstream, and
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settle onto the riverbed, and eventually reach organisms that depend on the river to
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reproduce.
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So if thawing permafrost due to climate change is helping to drive this process, does that
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mean every arctic river is going to turn orange?
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The short answer is no, geology is just as important as the climate.
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Warming can thaw the ground, it can deepen the layer that melts each summer, and it can
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open up new pathways for groundwater.
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But none of that automatically produces acid or releases metals.
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For that to happen, the right minerals have to be there in the first place.
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Think back to the pyrite we talked about earlier, if groundwater begins reaching rock that
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contains a lot of sulfide minerals, then oxygen and water can trigger those chemical reactions.
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Sulfuric acid can form, and iron and other metals can be released.
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But if the underlying geology is different, thawing permafrost may produce a completely
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different chemical response, or none at all.
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So climate change is not simply turning arctic rivers orange, it's changing the access.
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It's allowing water and oxygen to reach parts of the ground that were previously off
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limits, frozen off from the surface.
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What happens next depends on what is buried there.
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The landscape matters.
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Sometimes watersheds contain minerals that can neutralize the acid.
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Others don't.
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Some have large rivers that are capable of diluting incoming water.
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Others are just made up of small streams, where even one acidic seap can have a large
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effect.
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And groundwater doesn't move the same everywhere, it follows cracks and slopes and soil
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layers and underground channels.
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That means two neighboring valleys experiencing similar warming can respond very differently.
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Rivers and one may appear clear, while in the other they may begin changing color in
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just a few years.
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That's one reason scientists are trying to map where these vulnerable areas are located.
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Satellites can help identify streams that have changed from clear to orange.
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Aircraft and drones can survey remote watersheds.
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Scientists on the ground can collect water samples to measure the acidity, the sulfate concentration,
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the iron and other trace metals.
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And long-term monitoring stations can show when a river's chemistry begins shifting.
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Researchers are also looking beyond Alaska.
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Permafrost exists in enormous areas of Canada, Greenland and Siberia.
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And many of those landscapes contain similar mineral deposits.
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So one of the questions scientists are asking is whether the rusting rivers of Alaska are
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just a local oddity, or an early example of something we may begin seeing elsewhere
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across the Arctic.
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We don't know the answer yet, but the rapid change is already documented in parts of
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the Brooks Range, show just how quickly a watershed can respond if the right conditions
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line up.
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That might be the most surprising part of this story.
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Climate change is often described in terms of temperature, a warmer atmosphere, a warmer
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ocean and melting ice.
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But warming changes where water flows underground.
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It can expose minerals that were previously sealed away, in some cases, for millennia.
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And they can trigger chemical reactions that were largely dormant.
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And those reactions can then move from rock to groundwater to rivers and eventually to
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entire ecosystems.
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Climate change didn't create the iron, it didn't create the pyrite.
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That was already there.
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What it changed was the access.
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And sometimes unlocking something that's been frozen for thousands or even millions of
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years can completely change the river that's flowing above it.
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A river turning orange may look like a pollution story, but in Arctic Alaska, the source can
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begin at far beneath the surface.
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Thawing ground opens new pathways for water, water reaches minerals that were once frozen
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away and chemistry takes over.
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The effects can travel from rock to groundwater to rivers and eventually an entire ecosystem.
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While climate change does not create those minerals, it is changing the conditions that
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allow them to react and providing yet another example of just how complex the world is
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that we live on.
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I'm Dr. Mac and this has been The Climate Translation.
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If you have a question about the climate you've been too afraid to ask or if you have
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a differing opinion, I want to hear from you.
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I can use your viewpoints in future episodes.
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You can reach me at theclimatetranslation at gmail.com.
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I'll see you next time.