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Researchers detect warming trend in northern Idaho streams

Warmer water temperatures being recorded in northern Idaho streams and rivers are creating unhealthy conditions for trout, especially the region’s Westslope cutthroat population, Idaho environmental officials said.

A recent analysis by the Idaho Department of Environmental Quality shows that nearly 900 miles of streams in Kootenai and Shoshone counties are reaching temperatures up to 80 degrees in warmer months, well above the optimal temperature of 55 degrees or colder for trout species.

“That’s pretty warm even for people. So it’s very warm for trout,” Kajsa Stromberg, DEQ spokeswoman, told the Coeur d’Alene Press in a story published March 12.

The biggest factor to the warming trend is excessive sun exposure and lack of tree cover that provides shade and protection, she said. The region most affected by the warmer waters is the North Fork Coeur d’Alene River Sub basin, a region popular for anglers and prized for its population of cutthroat trout.

The warmer temperatures have a variety of negative impacts on trout, from making the fish lethargic to heightened risk and exposure to potentially threatening disease.

“They’re a very popular fishery. Very popular with the anglers,” Stromberg said of the streams. “And for a lot of people, just the fact that they’re out there is important. They’re really beautiful.”

To help reverse the trend, the DEQ is proposing a plan to lower water temperatures and improve access to colder, deeper waters.

The strategy includes building more rock structures and logs to narrow and deepen channels and improving access fish have to cold-water channels and natural springs. The plan, now open for public review and comment, would also protect more of the region’s shoreline trees from timber harvest managed by the U.S. Forest Service.

“Some of it is going to be something that will be voluntary, carried out by landowners,” Stromberg said of channel and shoreline work. “We could go into a cost-sharing agreement for planting, or they could plant trees on their own.”

The agency is taking written comments on the proposal until April 10, followed by a public hearing. The agency will also submit its draft plan to the Environmental Protection Agency for review.


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