The Army Corps of Engineers released cold water from Dworshak Dam on July 25 as rivers across central Idaho climbed to dangerous temperatures for salmon and steelhead, threatening the survival of fish species crucial to the region’s ecosystem and tribal heritage.
The Clearwater River near Orofino reached 79.7 degrees that day, while the Snake River 25 miles southwest of Lewiston hit 74.4 degrees—both well above the 68-degree threshold where the sensitive fish species begin exhibiting stress responses. The two rivers converge at Lewiston, creating a combined waterway where elevated temperatures pose a particular threat to migrating populations.
Salmon and steelhead show measurable signs of biological distress once water temperatures exceed 68 degrees, according to Chris Peery, a fish biologist with the Corps of Engineers. “Above about 68 degrees, they start showing signs of stress, migration delay, and, if temperatures go higher, mortality can start to occur,” Peery said.
Strategic Use of Deep Reservoir Water
Dworshak Dam, one of the nation’s tallest structures at 717 feet, holds the key to this cooling strategy. The 717-foot-tall facility ranks as the third tallest dam in the United States and contains more than 3.4 million acre-feet of water storage capacity. A critical advantage of the reservoir lies in its thermal properties: water drawn from the dam’s depths remains at approximately 42 degrees year-round, providing a reliable source of cold water during summer heat events.
The Corps coordinated the water release with both the National Marine Fisheries Service and the U.S. Fish and Wildlife Service before opening the gates. The effort successfully maintained river temperatures behind Lower Granite Dam at 66.1 degrees or cooler—within the acceptable range for threatened fish populations.
Peery emphasized the delicate balance required in managing the resource. “If we manage it carefully, we can help cool the Snake River so it stays around 68 degrees in the tailrace of Lower Granite Dam, but there is a limited amount of water that we can release from Dworshak,” he explained.
The Dworshak Infrastructure Challenge
Dworshak Dam has served the region since construction began in 1966. Its massive height—designed for flood control and hydropower generation—made it physically impossible to construct a traditional fish ladder, creating a permanent barrier for anadromous fish attempting to migrate upstream. This design limitation underscores why managing downstream water temperatures has become such a critical tool for fish conservation.
The U.S. Fish and Wildlife Service and the Nez Perce Tribe jointly operate Dworshak National Fish Hatchery, which works to sustain populations of threatened species. The hatchery program, combined with strategic water releases during heat events, represents the primary approach to managing salmon and steelhead survival in the region.
What Comes Next
The Corps of Engineers will continue monitoring river temperatures throughout the summer season. Heat events remain a recurring challenge in Idaho’s river systems, with climate patterns and water availability driving the need for ongoing coordination between federal agencies and tribal partners. Future warm-weather periods will likely trigger similar releases from Dworshak, making the dam’s cold-water capacity an increasingly important management tool for protecting anadromous fish populations in central Idaho.
Residents and water managers across the region rely on real-time temperature monitoring and coordinated releases to balance hydropower production, flood control, and fishery preservation—a complex equation that requires careful planning and limited resources.