Officials will not release cool water from a Colorado River reservoir to protect threatened fish

Federal officials said Thursday they will not release cool water this year from one of the Colorado River's major reservoirs, which would have protected a threatened native fish downstream but put more strain on already struggling hydropower production.

In an email obtained by The Associated Press, the Bureau of Reclamation told various groups that water from Glen Canyon Dam in northern Arizona would not be released “due to significant hydropower generation concerns under already strained system conditions."

As the Colorado River and its once massive reservoirs shrink from overuse and climate change, officials were faced with a decision that pits conservation of the humpback chub — a threatened fish native to the river — against ratepayer costs for electricity.

The decision comes after the worst snowpack on record for the Colorado River Basin, relied upon by farmers, industries, wildlife, hydropower and more than 40 million people in seven U.S. states, tribal nations and Mexico. It also comes a week after federal officials announced a proposal to stave off a crisis in the beleaguered waterway.

Officials stepped in after states that rely on the river — California, Colorado, Arizona, Nevada, New Mexico, Wyoming and Utah — failed to reach an agreement on how to share the dwindling resource long-term. Under the proposal, California, Nevada and Arizona would share water cuts.

A “cool mix flow" is when cold water is released from deep in a reservoir — in this case Lake Powell — to cool the river below. There are no hydropower turbines in the cool, deep section, so significant power generation would have been lost.

Lake Powell is about 23% full after decades of overuse and evaporation of water as average temperatures rise because of climate change. With such a low reservoir, warm water near the surface gets sucked through the generators and sent downstream.

Smallmouth bass, introduced in Lake Powell in the 1980s for sport fishing, live at that warm surface and also get sucked through the hydropower generators and into the river below, and if it's warm enough, they spawn. That’s a problem for the humpback chub and other federally protected fish farther south on the river.

Officials say cool water releases from Lake Powell in 2024 and 2025 successfully prevented smallmouth bass spawning.

The river downstream of the dam is about 69 degrees Fahrenheit (20.5 degrees Celsius). The Bureau says it considers recommending cold water releases when the average daily temperature there exceeds about 60 F (15.5 C) for three consecutive days. Those temperatures have regularly exceeded that threshold for more than a month.

“Our efforts this year will continue to focus on expanded rapid response removal actions, additional backwater modifications, evaluation of innovative tools, and advancement of durable structural solutions,” wrote Wayne G. Pullan, the agency’s regional director of the Upper Colorado Basin, in the email.

Matt Rice, director for the southwest region for the conservation group American Rivers, said the decision was not unexpected but still disappointing.

“We’ve proven that the cool mix flows are the most effective way to mitigate the smallmouth bass invasion in the Grand Canyon," he said. “Hopefully it’s not a death sentence to humpback chub." He added that the elevated temperatures are also life-threatening for the nearby rainbow trout fishery.

He said American Rivers hopes for collaborative and innovative solutions in the future that balance protecting the environment while managing the river for the people who rely on it for power.

Utilities that buy hydropower from Glen Canyon Dam said releases would have forced them to spend millions of dollars to buy alternative energy that is more costly and less likely to be renewable, and could increase electricity bills for customers.

“We’re very pleased with the decision and appreciate Reclamation's deliberate and thoughtful approach to this, just recognizing the challenges that we’re facing on the river,” said Andy Colosimo, executive director of the Colorado River Energy Distributors Association, which represents about 155 customers who buy federal hydropower generated from the river. “I think this was the right call, given the conditions that we’re all facing.”

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