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Researchers are paying close attention to waterways in some other parts of the country. Freshwater rivers and streams are not so fresh any more. Their chemistry is changing. Scientists have found dozens of waterways along the East Coast that are becoming more alkaline, less acidic.

As NPR's Christopher Joyce reports, new research shows this trend to be surprisingly widespread, with possibly harmful consequences.

CHRISTOPHER JOYCE, BYLINE: Let's go back to 1963 for a minute. In a New Hampshire forest, a young scientist named Gene Likens found a stream that was incredibly acidic like tomato juice. Likens eventually found the culprit: acid rain, industrial air pollution raining down from the sky. It was killing trees and streams in the East. Now 50 years later, there's less acid rain. But Likens and other scientists are finding that many rivers are now becoming the opposite of acidic- they're becoming alkaline, and it seems to be happening all over the place.

GENE LIKENS: The real shocker to me was we found it from New Hampshire to Florida, and rivers and streams that drained agricultural land, forest land, urban land.

JOYCE: Likens and his team has found that two-thirds of the 97 streams and rivers they studied in the East have been growing more alkaline, from the mighty Susquehanna to small urban streams like this one, Gwynns Falls in downtown Baltimore, Maryland.

SUJAY KAUSHAL: So we can climb down in there.

JOYCE: Sujay Kaushal walks down slope to the stream, directly below an overpass of Interstate 95. Kaushal teaches geology at the University of Maryland and works with Likens. This stream is where he first found signs of rising alkalinity.

KAUSHAL: We couldn't explain it. At first we thought it was simply just, there's more concrete and cement and that's causing it. One of key ingredients of concrete is actually limestone.

JOYCE: When rain and limestone come into contact, the runoff can contain a lot of bicarbonate, basically the stuff you take for acid indigestion. Its alkaline. Maybe that was polluting the stream.

But when Kaushal and Likens looked at waterways elsewhere - in forests, in farmland, they found they too have been growing more alkaline for the past 25 years.

And the really surprising thing is it appears acid rain is doing this. It's been eating away at rocks, especially limestone rocks, and that produces bicarbonate that runs down into rivers.

KAUSHAL: We're basically dissolving the surface of the Earth. It's ending up in our water. It's like rivers on Rolaids. There's a natural antacid in these watersheds.

JOYCE: Now, that's not an immediate health threat, but it does have environmental effects. Kaushal invites me to wade into the stream. Mops of stringy green stuff coat the rocks. It's thick and slippery underfoot.

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KAUSHAL: You can feel that?

JOYCE: Yeah.

KAUSHAL: OK, all that scum, all that slime is algae and bacteria. And the alkalinity actually can stimulate growth of certain types of algae.

JOYCE: Too much algae will suck the oxygen out of the water - bad news for whatever lives in it.

Another thing about alkaline water, if it mixes with sewage, it creates a toxic stew. And it just so happens, there's a sewage leak just upstream of us.

KAUSHAL: So why don't we, why don't we walk up along this...

JOYCE: I'm not going to walk in it.

KAUSHAL: OK, you're not? I can't get you to go in there? It can be highly dangerous.

JOYCE: I kinda figured that.

Now, Gwynn's Falls is a small stream, it doesn't take a lot to alter its chemistry. But even big rivers are growing more alkaline.

PETER RAYMOND: We've changed the chemistry of the Mississippi. These aren't small systems.

JOYCE: Ecologist Peter Raymond at Yale University found that the country's biggest river is also growing more alkaline. He says it's not clear what kind of damage all this is doing.

RAYMOND: It can be pretty important, I think, for a lot of different freshwater organisms. But, you know, for some are winners and some will be losers.

JOYCE: If there's any good news here, it's this: there's less acid rain now. But enough, says Gene Likens, to keep eating away the rock. Likens, who's now at the Cary Institute of Ecosystem Studies, says he never dreamed acid rain would have such a long reach.

LIKENS: The impacts are large, they're larger than we ever thought 50 years ago, they might be, I must say.

JOYCE: The research is published in the journal Environmental Science and Technology.

Christopher Joyce, NPR News.

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In Northern California, firefighters say they have now mostly contained a fast-moving wildfire that destroyed scores of homes. The fire began Monday 150 miles north of Sacramento. At its peak, the fire was sweeping through rural communities at a rate of 500 acres an hour.

INSKEEP: Also almost completely contained now is the month-old Rim Fire, which has burned almost 400 square miles in and around California's Yosemite National Park. Officials say that fire should be fully contained by late next week.

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