Federal water managers are weighing a plan to release cold water from the depths of Lake Powell through Glen Canyon Dam, a move designed to cool the Colorado River and shield the threatened humpback chub from predatory fish, but one that would come at the direct expense of hydropower production, according to agency officials and documents reviewed by the Associated Press.
The proposal, known as a cool mix flow, would draw water from the reservoir’s deepest layers, where temperatures are low enough to disrupt the spawning and survival of non-native fish that prey on the chub. However, those deep layers sit below the dam’s hydropower intakes, meaning the water would bypass the turbines entirely, the AP reported, sacrificing a significant share of the dam’s generating capacity.
The trade-off arrives during the worst snowpack on record for the Colorado River Basin, which feeds Lake Powell and supplies water to more than 40 million people in seven states, tribal nations and Mexico. Shrinking flows already threaten the region’s farms, cities and hydroelectric output, intensifying pressure on officials to balance competing demands.
Complicating the decision, the seven basin states have been unable to reach a long-term agreement on how to share the river’s dwindling resources after the current management guidelines expire at the end of 2026. The failure to negotiate a successor pact leaves dam operators and wildlife managers without a clear policy framework for weighing conservation measures like the cool mix flow against the electricity needs of Western ratepayers.
The humpback chub, a native Colorado River fish that evolved to thrive in the Grand Canyon’s cold, sediment-rich waters, was listed as threatened under the Endangered Species Act. Its numbers had rebounded in recent decades after dams and non-native predators decimated the population, but warming river temperatures and persistent predator pressure have once again put the species at risk, prompting the Bureau of Reclamation to study the cool-water release as an emergency measure.
Any reduction in hydropower output from Glen Canyon Dam would ripple through regional electricity markets that depend on the dam for a portion of their carbon-free supply, potentially raising costs for consumers in Arizona, Nevada and California. For now, officials are evaluating the ecological benefits against those economic costs, with a decision expected in the coming months.