Environmental

Reclamation using cold water to disrupt nonnative fish spawning below Glen Canyon Dam

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Reclamation using cold water to disrupt nonnative fish spawning below Glen Canyon Dam

The Bureau of Reclamation has begun releasing deeper, and therefore colder, water from Lake Powell through Glen Canyon Dam to disrupt the establishment of smallmouth bass, which could negatively affect populations of threatened humpback chub, below the dam.

Glen Canyon Dam impounds Lake Powell, the largest storage unit of the Colorado River Storage Project, and provides water for a 1,320 MW hydroelectric powerhouse.

The need for these flows was triggered after the average observed daily water temperatures reached smallmouth bass reproduction thresholds above 15.5 degrees Celsius (60 degrees Fahrenheit) at the confluence of the Colorado River with the Little Colorado River.

The declining elevation of Lake Powell has led to the release of warmer water from Glen Canyon Dam. Invasive fish, such as smallmouth bass, residing in the upper layer of Lake Powell are more likely to pass through the dam and spawn downstream. If left unchecked, they could continue to expand their population. Smallmouth bass are known to prey on native fish species in the Grand Canyon that are protected by the Endangered Species Act.

“The most healthy and vibrant populations of humpback chub are found in the stretch of the Colorado River downstream of Glen Canyon Dam that runs through the Grand Canyon,” said Reclamation Upper Colorado River Basin Regional Director Wayne Pullan. “We have a great interest and commitment to preserving our progress in recovering the humpback chub and protecting all native fish species within the Grand Canyon. And this summer, by using these cooler flows, we have our best operational chance to achieve these goals.”

The ‘cool mix flow’ consists of releasing water from the hydropower penstocks, as well as the river outlet works about 100 feet below the penstocks. This cool mix approach was the selected alternative in the recent Record of Decision for the Glen Canyon Dam Long-Term Experimental and Management Plan Final Supplemental Environmental Impact Statement.

Earlier this year, Reclamation established interim guidelines on Glen Canyon Dam, addressing reduced capacities for the river outlets when the reservoir level is low, due to the increased risk of cavitation at elevations of 3,550 feet or below. With Lake Powell’s elevation above this threshold, the river outlets will operate safely and under normal conditions, with no elevated cavitation risk. Additionally, scheduled recoating work will proceed as planned, as only one of the four river outlets can be recoated at a time and only two river outlets will be in use at any given time for the cool mix flows.

Reclamation will continue to work with the Western Area Power Administration to minimize the impacts of reduced power generation to customers by adjusting the timing of these releases. Reclamation will also continue to work with its partners to develop and implement additional preventative actions to combat non-native species in the Colorado River.

Considerations will be made for possible conditions that temporarily or permanently suspend this action, including risks that impact grid reliability, system disturbances, and emergencies or effectiveness of controls on smallmouth bass, Reclamation said.