MARY LOUISE KELLY, HOST:

Now to a story from the Rocky Mountains of Colorado, where climate change is having a subtle but serious impact on streams and rivers. As member station KUNC's Rae Solomon reports, they're becoming more acidic and polluted with heavy metals like zinc, iron and copper.

RAE SOLOMON, BYLINE: It's a bright summer day in the mountains. Research geologist Andrew Manning and some colleagues are hauling sensors, buckets and other scientific equipment through thick scrub willow at the edge of a rushing mountain stream.

ANDREW MANNING: We are on the upper Snake River in the Colorado Rockies here at about 11,000 feet.

SOLOMON: The upper Snake doesn't look like a clear mountain stream. Instead, it has a distinct reddish hue. That's because the water is depositing iron onto the river bed.

MANNING: This is kind of a unique stream in that it has unusually high metal concentrations and high acidity.

SOLOMON: Manning, who works for the U.S. Geological Survey, is here to keep tabs on those unusually high metals and acidity, a phenomenon known as acid rock drainage. His research points to sharp increases.

MANNING: We look specifically at zinc and copper. It amounts to about a doubling of concentrations over the past three decades, and that's substantial.

SOLOMON: Manning says it's all happening because of changes in the climate. Ground that is normally frozen year-round is now thawing and the water table dropping.

MANNING: You have large zones of the subsurface that never saw any water or oxygen because they're armored off by a frozen ground layer or under the water table.

SOLOMON: But when the ground thaws or the water table drops, new rock high in sulfates is exposed to the elements. That makes the water acidic and allows heavy metals to leach out and flow into the waterways. That can kill plants, insects and fish.

ASHLEY RUST: Of the water quality problems I deal with, this is the largest scale and the most daunting.

SOLOMON: Ashley Rust is a water quality specialist with Colorado Parks and Wildlife. She says acid rock drainage is devastating to river ecosystems.

RUST: It can dissolve tissue. It can dissolve shells. Like, the exoskeleton or the outside of an insect's body is made of, like, calcium carbonate material, and so the low pH will dissolve it, and so the insects can't live.

SOLOMON: As the effects intensify, Rust worries about a future with more silent waters stripped of life. And it's not just in Colorado. Researchers in Alaska have been seeing similar issues in waterways near thawing permafrost, the Arctic's so-called rusting rivers. Research chemist Amanda Barker is with the Army Corps of Engineers Cold Regions Research and Engineering Lab.

AMANDA BARKER: Literally the water looks orange. You're seeing, you know, impaired waterways that are just bright orange, and that's oxidized iron.

SOLOMON: She says they don't know yet how widespread this problem is. But...

BARKER: Anywhere you have permafrost that is thawing, you're likely going to see the waterways being impacted because you're exposing fresh mineral surfaces to weathering reactions.

(SOUNDBITE OF WATER SPLASHING)

SOLOMON: On the upper Snake, Andrew Manning and his colleague Sara Warix crouch at the river's edge, dropping a probe that measures acidity into the swirling water.

SARA WARIX: So our pH is 3.88.

SOLOMON: They also collect water samples in plastic bottles. They'll take those back to the lab to analyze the metal content. Manning says beyond ecosystem damage, if levels continue to rise, that could mean problems for drinking water.

MANNING: A lot of our mountain communities get their water resources from these streams. And if you begin to increase the metals enough high up and you can't dilute it very well anymore, now they may have to start treating that water or taking it out in a different place.

SOLOMON: He says municipal water managers would be wise to take note. For NPR News, I'm Rae Solomon in Summit County, Colo.

(SOUNDBITE OF FUGEES SONG, "READY OR NOT" ) Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.