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Rising Yakima River temperatures pose threat to salmon

YAKIMA – With water flows down and the heat up, temperatures in parts of the Yakima River this summer have been running more like those in the waters of coastal Hawaii, according to the Washington Department of Ecology.

The conditions, which pose a threat to salmon, have prompted a group of researchers and citizens to float the river to find areas of cooler water where fish can gather during migrations, Ecology said in a news release. The havens might prove crucial to fish survival.

Researchers are profiling the havens to compile data for the lower 100 miles of the river in an effort to meet environmental objectives of the Yakima Basin Integrated Plan. Ecology, the Benton Conservation District, Yakama Nation and U.S. Geological Survey are involved in the effort.

The plan is an effort to solve decades of water conflicts in the Yakima River Basin with a 30-year vision to respond to drought and changing climate. Its goal is to ensure water is clean and ample, and lands are protected and productive for communities and the natural environment.

Low flows and 100-degree days brought the average daily water temperature in the lower Yakima River near Prosser above 80 degrees for 12 days in July, well above the historical mean average of 69.3 degrees for the month, Ecology reported. Twenty of the top 30 daily average river temperatures recorded at Prosser since 1990 have occurred over the past four years.

National Oceanic and Atmospheric Administration fisheries biologist Sean Gross said conditions likely mean more threats from predators for juvenile salmon, or smolts, heading out to the ocean. Evidence has also shown adult sockeye delay migration upstream because they won’t travel to spawning areas in water above 68 degrees. Temperatures of 73-77 degrees are considered lethal to salmon.

“There are consequences to delaying like that,” Gross said. “For them to wait out there, they’re subject to more mortality and then when they’re moving through warm water there are stresses particular to warm water.”

Benton Conservation District water resources specialist Marcella Appel is leading the team floating the river and searching for cool-water refuges, which could allow sockeye, fall chinook and other species of salmon to move upstream more quickly. Those cooler pockets are often created by irrigation or shallow groundwater flows.

“In some places we’ll see kind of an effect where it’ll buffer the warming,” Appel said. The salmon “are amazingly good at being able to kind of cue in at what’s going to be a trade-in and help them get through.”

But Gross cautions that any gains made by identifying cool spots could be “around the margins,” perhaps allowing salmon to move upstream just a week or two faster.

Identifying those areas from Wapato to where the Yakima flows into the Columbia River in the Tri-Cities requires nine daylong float trips with three boats of two people each to measure the middle and along both banks.

Appel said the Yakama Nation handled the section from Wapato to Mabton, while she enlisted help from the NOAA, Columbia fisheries and local citizens for the remainder of the river. A float from Prosser to the Chandler Power Plant west of Benton City is scheduled for September, and similar efforts to collect data along the same 100 miles are planned for next summer.

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