The Colorado River below Glen Canyon Dam is running about 70 degrees Fahrenheit (21 degrees Celsius) at Lees Ferry, about 16 miles downstream of the dam. That is well above the 60-degree mark at which invasive smallmouth bass spawn. For the past two summers, federal managers released cold water from deep in Lake Powell to cool the river and limit bass reproduction. This year, they are not.

In an August email to stakeholders, the Bureau of Reclamation said it would not make the so-called cool-mix release "due to significant hydropower generation concerns under already strained system conditions," The Associated Press reported on the cool-water decision. The AP put Lake Powell at about 23 percent full at the time, after decades of overuse and a record-poor snowpack in the basin.

The choice sets electricity against ecology. Cool-mix releases draw water from deep in the reservoir, below the level of the dam's turbines, so the dam generates less power. Skipping them protects hydropower for the utilities that buy it. It also leaves the humpback chub, a native fish that took decades and tens of millions of dollars to bring back from the brink, more exposed to a predator.

Why Warm Water Changes Everything at Glen Canyon Dam

The problem starts at the top of Lake Powell. Smallmouth bass live in the reservoir's warm surface layer. As the lake has dropped, that warm layer has reached the level of the penstocks, the intakes that feed the turbines, according to KUNC and Circle of Blue. Warm water now flows into the river below, and biologists fear more bass will be carried through with it.

The river crossed the 60-degree spawning mark in June. Under the dam's operating plan, three consecutive days above 60 degrees are supposed to trigger a cool-mix release. In its 2026 Fish and Wildlife Service biological opinion for Glen Canyon Dam, the U.S. Fish and Wildlife Service called cool mix the "only conservation measure proven to limit smallmouth bass reproduction." Officials told the AP that the 2024 and 2025 releases successfully prevented smallmouth bass spawning, and KUNC reported that those releases knocked down bass numbers.

The stakes for the chub are high. The fish was listed as endangered in 1967, and after decades of conservation work, the Fish and Wildlife Service reclassified it as threatened in 2018. Smallmouth bass readily prey on other fish, and biologists have long warned that an established bass population below the dam could erode those gains.

The dry year has also blocked another environmental release. Reclamation has not conducted a high-flow release to rebuild Grand Canyon's eroding beaches since 2023, even though there is enough sediment in the river to warrant one. USGS data presented in August, including a USGS sediment update showing shrinking Grand Canyon sandbars, indicated that a typical sandbar is now smaller than in 2016. A decision on a fall release is expected within weeks, and experts told KUNC one is highly unlikely.

Utilities, Conservationists and the Cost of Cold Water

The utility argument centers on cost and reliability. The 2025 cool-mix flow cost the Western Area Power Administration, which markets federal hydropower, $6.1 million to replace lost electricity for its contractors, KUNC reported. Utilities told the AP that another release would have forced them to spend millions buying alternative power that is more costly and less likely to be renewable, which could raise customer bills.

"I think this was the right call, given the conditions that we're all facing," Andy Colosimo told the AP. Colosimo is executive director of the Colorado River Energy Distributors Association, which represents about 155 customers who buy federal hydropower generated from the river. Glen Canyon's generation is already down more than 40 percent from when Lake Powell was full, according to KUNC.

Conservation groups argue that the law requires balance. The Grand Canyon Protection Act of 1992 directs Reclamation to operate the dam in ways that protect the canyon's natural and cultural resources and visitor use. "I don't feel like they're being balanced right now," Jen Pelz of the Grand Canyon Trust told KUNC. Matt Rice of American Rivers told the AP that cool-mix flows have proven to be the most effective way to fight the bass invasion. River guides say shrinking beaches also crowd rafting trips.

Reclamation says it is pursuing other tools. In the short term, crews are stunning bass with electrofishing equipment and removing them from the water. Over the longer term, the agency is considering what it calls durable structural solutions, including infrastructure to regulate the temperature of water passing through the dam. Such infrastructure would take time and money to build, and electrofishing has not been shown to match cool mix at limiting spawning.

The fish decision is part of a larger infrastructure problem. The dam, which KUNC described as the Colorado River basin's most significant water-supply choke point, relies on turbines because its other outlets are untested over long periods and were damaged in a previous high-flow release. Lower basin states and tribes have asked for upgrades, and Reclamation is assessing three options in a study expected in early 2027. Any additional action would require congressional approval and funding.

What Comes Next for the Chub and the River

Scientists say the old management rules may no longer fit. "Everything was developed in a world of full reservoirs," Jack Schmidt of Utah State University's Center for Colorado River Studies told KUNC. "And now the reservoirs are empty." He argued that the river's ecosystem has changed so much that its management goals need to be revisited.

The evidence has limits. The cool-mix record rests on only two years of releases, and it is not yet known how many bass will spawn below the dam this year or how far they could spread toward the chub's core habitat downstream in Grand Canyon. Reclamation has not released detailed results from this year's removal efforts, and reservoir levels have continued to change since August.

For households, the connection runs through power bills and public lands. Utility customers who rely on federal hydropower from the Colorado River may face higher costs when that power is reduced. Grand Canyon rafters and visitors will see the effects on beaches, campsites and the river's native fish.

The next milestones are Reclamation's decision on a fall high-flow release and results from this year's bass removal and fish surveys. The infrastructure study is due in early 2027. Nature World News will follow Reclamation, Fish and Wildlife Service and USGS updates as the agencies release them.

What Readers Want to Know

What is a cool-mix release?

It sends cold water from deep in Lake Powell, below the turbine intakes, and mixes it with warmer water from the turbines. The goal is to keep the river too cool for smallmouth bass to spawn.

Why did Reclamation skip it this year?

Reclamation cited significant hydropower generation concerns under already strained system conditions. The release reduces how much electricity the dam produces.

How full is Lake Powell?

The AP reported it was about 23 percent full in early August. Levels change over time, so check Reclamation's current reservoir data.

Why are smallmouth bass a threat?

They prey on other fish, including the threatened humpback chub. Warm water drawn from a lower Lake Powell lets them survive and spawn below the dam.

What is Reclamation doing instead?

Crews are using electrofishing to stun and remove bass, and the agency is considering long-term infrastructure to control the temperature of water released from the dam.

Could this affect my electric bill?

Utilities that buy federal hydropower say replacing lost generation costs millions, and those costs can reach customers. Skipping cool mix avoids that expense this year.

When will more be known?

A decision on a fall high-flow release is expected within weeks. Reclamation's infrastructure study is expected in early 2027.