HEYBURN • The U.S. Bureau of Reclamation started increasing water flows to the Snake River below the Palisades Dam on Thursday to benefit native fish between Palisades Reservoir and Shoshone Falls.
The faster, deeper flow will give native cutthroat trout an advantage over the invasive rainbow trout that find their way upstream from the Shoshone Falls area, said Michael Beus, of the Bureau of Reclamation office in Heyburn.
The bureau has been increasing flows yearly since 2004.
“The increased water flow tends to trigger the cutthroat to travel up the tributaries to spawn,” said Dan Garren, Idaho Falls fisheries manager for the Idaho Fish and Game Department. “Research since the 2000s shows that when we have high water flows similar to natural run-off conditions, the cutthroats tend to do better.”
Rainbow and cutthroat trout spawn at the same time and will cross-breed, Garren said. The rainbows tend to be more aggressive and feed on cutthroat eggs and offspring, harming that fish population.
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Idaho Fish and Game has been working for years to increase cutthroat trout in the Snake River’s south fork area.
Water flows now are being increased by 10 percent daily until the maximum flow,18,500 cubic feet per second (cfs) is reached.
The bureau is warning water users to exercise caution, as these will be the season’s highest flows, combining water released from the dam with seasonal snowmelt that naturally creates a fast, cold, high flow.
Starting Monday, the flows will be cut by 5 percent a day until a seasonal norm of 13,000 cfs is reached, Beus said.
The flow increase won’t affect the bureau’s ability to deliver required water to farmers for irrigation, officials said.