The U.S. government is weighing a proposal that would protect endangered fish in the Grand Canyon stretch of the Colorado River by releasing cooler water from Lake Powell, a move critics say would cut hydropower generation and raise costs for ratepayers.
In northern Arizona, Glen Canyon Dam sits between Lake Powell—one of two major Colorado River reservoirs—and a roughly 278-mile stretch of river farther south that is part of the Grand Canyon. Under the proposal discussed by agencies, operators would use a “cool mix flow,” releasing cold water from deeper in Lake Powell to cool the river below the dam. The plan’s central tradeoff is that the cold water comes from portions of the reservoir that lack hydropower turbines, meaning significant power generation would be lost.
Environmental advocates and fish managers argue that without cool releases, warm downstream water projected for this summer would create conditions in which non-native predatory fish can reproduce. John Berggren, regional policy manager for the environmental nonprofit Western Resource Advocates, said, “There is a limited water supply. It’s getting even lower. And with that, a lot of hard decisions need to be made.”
The decision has been shaped by the basin’s water outlook. The proposal arrives after the worst snowpack on record for the Colorado River Basin, a system relied upon by farmers, industries, wildlife and more than 40 million people across seven U.S. states, tribal nations and Mexico. It also comes as states have not reached a long-term agreement on how to share the river beyond this year, when current guidelines expire.
Officials have said the Bureau of Reclamation is weighing several factors, including ecological health and the dam’s hydropower production. The Interior Department, which oversees the bureau, declined to comment. If a cool-water release is approved, officials said it would likely take place from June to October through jet tubes that bypass turbines near the warmer surface.
Proponents point to how declining reservoir levels change the water that passes through turbines. Lake Powell is at about 23% of capacity after decades of overuse and evaporation driven by rising temperatures. Officials say warm water near the surface is then pulled through generators and sent downstream. They also note that smallmouth bass—introduced into Lake Powell in the 1980s for sport fishing—can be sucked through hydropower generators and into the river below, where they feed on humpback chub in the upper river section and are expected to pose a wider risk as conditions warm.
Agencies say water temperatures just downstream of Glen Canyon Dam are expected to break records set in 2022, when smallmouth bass were first found there. Officials project that water will consistently exceed 60 degrees Fahrenheit (15.5 Celsius) by mid-June due to warm water being pulled from Lake Powell. They say temperatures higher than that could allow non-native predatory fish passing through the dam to reproduce, including through spawning downstream. Officials also say cool-water releases in 2024 and 2025 successfully prevented spawning.
At a recent meeting on managing the issue, Heather Whitlaw, field supervisor with the U.S. Fish and Wildlife Service, warned that the conservation strategy depends on cooling the system rather than relying on after-the-fact removal of predators. She said, “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.”
Utilities that buy federal hydropower say the cool-water option would come with immediate generation losses and an expense to replace the electricity. The Utah utility group Heber Light & Power said that if the releases are approved, utilities could end up bypassing about half of generation at Glen Canyon Dam and purchasing power elsewhere. A letter to Interior Secretary Doug Burgum from the Colorado River Energy Distributors Association—an association that represents about 155 customers who buy federal hydropower—opposes the releases and says the cost of mitigation would be a recurring burden.
In the association’s view, the releases are not a sustainable long-term solution, and they could disrupt a critical fund used to operate, maintain and invest in hydropower and transmission facilities. The association also said it wants to understand remediation costs that it described in the letter as potentially exceeding $20 to $30 million per year, and it argued against the cool-mix approach as a strategy to prevent smallmouth bass reproduction.
Bureau of Reclamation data cited by utilities show how past cool-water releases affected hydropower. During the 2024 cool-water releases, nearly 900,000 acre-feet of water bypassed the generators, costing $19 million in replacement energy costs, the bureau said. It is unclear how much water would bypass the generators this year, utilities said, but replacement energy costs have been anticipated to be around $25 million, roughly the total cost to hydropower users from the previous two years.
For customers paying for replacement energy, the impacts are already visible in utility bills, according to the AP reporting. Emily Brandt, an energy resource manager with Heber Light & Power, said the utility has faced rate hikes over the past five years as generation declined due to drought and then further reduced because of what it called an environmental experiment. Ann Moulton, who lives in Heber City, said her residential electricity bill in April was $125.98, up from $103.24 and $86.14 for the same month in the previous two years. She said the changes have affected her budget, and the utility reported a jump in late payments this year from 10% to 12%.
Meanwhile, fishing guides and local businesses that depend on the river’s ecology are also watching the decision. Dave Foster, who has worked along the stretch of river between the dam and the start of the Grand Canyon since he was 13, said he remembers a 2022 die-off in Glen Canyon when warm water killed nearly half the rainbow trout the fishery relies on. He said guides have recovered unevenly since then, but that cool-water releases in recent years have offset some negative impacts and could be important for getting through fall and winter. Foster warned that if water becomes too warm after mid-June, bookings could be canceled and that “it will destroy it.”
The bureau is expected to announce its decision in the next couple of weeks, setting whether cool-water releases will be used from June to October to protect humpback chub and other federally protected fish—or whether agencies will instead rely more heavily on downstream removal efforts for predators.