Tuesday July 9, 2024

Bureau of Reclamation

As a result of warmer river temperatures, the Bureau of Reclamation will begin releasing deeper, and therefore, colder water on Tuesday, July 9 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. 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 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. The river outlet works are approximately 100 feet below the penstocks and can release cooler water downstream. This ‘cool mix’ approach was the selected alternative in the recently signed Record of Decision for the Glen Canyon Dam Long-Term Experimental and Management Plan Final Supplemental Environmental Impact Statement. 

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