NORTHERN ARIZONA — Federal officials are considering cool water releases from Glen Canyon Dam in northern Arizona this summer for the third consecutive year to protect the endangered humpback chub from predatory fish. The “cool mix flow” would release cold water from deep in Lake Powell to lower downstream temperatures and inhibit spawning by non-native predators.
Water temperatures below the dam are projected to exceed 60 degrees Fahrenheit by mid-June as warm surface water is drawn through hydropower turbines, creating conditions that allow smallmouth bass—introduced to Lake Powell in the 1980s—to survive passage and reproduce downstream. Roughly half the smallmouth bass that pass through the generators survive, and they already prey on humpback chub in the upper Colorado River. Officials project that without intervention, temperatures could surpass 2022 records when smallmouth bass were first found below the dam.
Cool water releases in 2024 and 2025 prevented predatory fish from spawning and helped sustain the trout fishery in Marble Canyon, which suffered a major die-off in 2022 due to warm water. “We are certainly just giving up on the future for any kind of recovery for humpback chub and all of the other pieces of the system that rely on those cooler water temperatures,” said Heather Whitlaw, field supervisor with the U.S. Fish and Wildlife Service.
However, the releases come at an energy cost. Since there are no turbines in the cold, deep portion of Lake Powell, water released through jet tubes bypasses power generation. In 2024, nearly 900,000 acre-feet of water bypassed generators, costing $19 million in replacement energy. This year’s cost is projected at $25 million. “We’re already seeing reduced generation from drought, and now we’re seeing even further reduced generation because of this environmental experiment,” said Emily Brandt, energy resource manager for Heber Light & Power.
Utilities argue the financial burden falls on customers, some of whom have seen rising electricity bills and increased late payments. The Bureau of Reclamation is weighing ecological and energy concerns and is expected to announce a decision within weeks. “There is a limited water supply. It’s getting even lower. And with that, a lot of hard decisions need to be made,” said John Berggren, regional policy manager for the environmental nonprofit Western Resource Advocates.