MARY LOUISE KELLY, HOST:

In the Northwest, salmon are struggling to make the seasonal migration upstream to their spawning grounds after a recent heat wave warmed up water temperatures. In fact, the water is so hot, biologists have dumped some salmon in trucks and driven them nearly 300 miles to cooler habitat. Northwest Public Broadcasting's Courtney Flatt has more.

COURTNEY FLATT, BYLINE: On the Snake River in far eastern Washington, sockeye salmon have had a rough summer. These fish swim 900 miles from the Pacific Ocean, up fish ladders, over eight dams, to their spawning streams in central Idaho. But here, about halfway through their journey, the water is too hot.

(SOUNDBITE OF WATER FLOWING)

DAVE VENDITTI: It's running 74 degrees. That's getting up to lethal temperatures for sockeye.

FLATT: That's Dave Venditti. He's a biologist with Idaho Fish and Game.

VENDITTI: They've had a series of tough breaks with weather and water condition.

FLATT: Venditti says that hot water causes salmon to pause their migration inland. It also increases their metabolism. And since salmon don't eat on their journey, they might run out of energy. Additionally, they can catch diseases more easily and have more trouble avoiding predators.

(SOUNDBITE OF WATER SPLASHING)

REBEKAH WINDOVER: Whoo. There we go.

To gather the sockeye, technicians gently guide fish into what's called a salmon sock. The sock is a slender, blue bag, about four feet long. It keeps the fish's gills wet while a technician carries it to a tank on the back of a truck.

WINDOVER: Yeah, arm and leg workout (laughter).

FLATT: Yeah.

That's Rebekah Windover, one of the technicians. From here, the fish hitch an eight-hour ride to cooler waters in central Idaho. This is the third time in less than 10 years biologists have hauled sockeye in this area to avoid hot water. Scientists say it's a peek into the future of a changing climate. Jay Hesse is a biologist with the Nez Perce Tribe, who rely on this stock of salmon for cultural and religious practices. He says less snowpack in the mountains means less water in Northwest rivers.

JAY HESSE: Low stream flows result in elevated water temperatures because of reservoir habitats that tend to heat up faster and retain that heat.

FLATT: Sockeye on the Snake River are some of the most endangered fish in the region. And the Nez Perce Tribe, along with other tribes and environmental groups, have advocated for several dams to be removed along this river. They say that would help with water temperatures and make salmon's migration easier. David Johnson manages the fisheries department for the Nez Perce Tribe. He says many tribal members rely on salmon for their primary food, nutrition and livelihoods.

DAVID JOHNSON: Salmon and these tribes are hand-in-glove. And, quite honestly, they've supported each other for countless years.

FLATT: Utility companies that use the dams for power, meanwhile, and farmers who rely on them for irrigation and barging, say the dams aren't the main reason salmon aren't doing well. They point to changing temperatures in the Pacific Ocean and a lack of shade along the river. Michelle Hennings is with the Washington Association of Wheat Growers. She says there isn't a silver bullet to protect these endangered fish.

MICHELLE HENNINGS: The dams are one issue. There's multiple issues that happen within why salmon could be at lower levels.

FLATT: Back at the Snake River, biologists add a few more fish to fill up the truck's tank and hop in the cab to start their drive.

(SOUNDBITE OF TRUCK STARTING)

FLATT: Venditti says it's a big responsibility to transport such precious cargo.

VENDITTI: It's nerve-wracking. It's not just fish. Yeah, it makes a long day even longer.

FLATT: This month, Venditti says they transported six truckloads of salmon. With forecasted 100-degree temperatures, the Snake River could stay warm for a while, but they likely won't truck anymore between now and the end of migration in August.

For NPR News, I'm Courtney Flatt on the Snake River.

(SOUNDBITE OF LUPE FIASCO SONG, "I'M BEAMIN'") Transcript provided by NPR, Copyright NPR.

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