October 9, 2023 — The Bureau of Reclamation announced last week the beginning of the formal process to devise future alternative operations for the Glen Canyon Dam. The purpose of these operations is to stop invasive fish from spawning downstream. The potential flow alterations are being considered for implementation through 2027.

Environmental Assessments and Public Feedback.

In August 2022, an environmental assessment titled “Glen Canyon Dam/Smallmouth Bass Flow Options” was undertaken by the Reclamation. The document was made public for feedback on February 24. After careful consideration of the environmental assessment and nearly 7,000 public comments, Reclamation determined that further analysis was needed

On June 6, further instructions came from the Glen Canyon Dam Adaptive Management Work Group. They instructed Reclamation to draft a supplemental environmental impact statement related to the December 2016 Glen Canyon Dam Long Term Experimental and Management Plan Record of Decision.

Lake Powell’s Ecosystem Challenges.

The water level of Lake Powell has been decreasing, and as a result, the epilimnion (the upper layer of the lake where most fish are found) is nearing the water intakes of the Glen Canyon Dam. This means invasive, non-native fish species, including the smallmouth bass, now have a higher probability of moving downstream into the Colorado River. The warm waters from the epilimnion increase the river’s temperature, creating favorable conditions for smallmouth bass to spawn. These bass pose a risk to the humpback chub and other native species.

Reclamation Commissioner CamilleTouton remarked, “We will continue our work to protect the river and its native species to the best of our ability as we plan our operations of the river. If smallmouth bass continue to spawn and establish below Glen Canyon Dam, there will likely be negative impacts to the humpback chub and other native fish species.”

Wayne Pullan, the Reclamation Upper Colorado Basin Regional Director, highlighted the organization’s obligations. He said, “Humpback chub were recently downlisted from endangered to threatened. However, in the Grand Canyon, the number of sub-adults has been low enough to trigger taking additional conservation actions to bolster the population by increasing survival and growth.”

It’s estimated that around 60,000 humpback chubs are below Glen Canyon Dam, with various segments located at different points along the Colorado River.

Future Plans and Public Involvement.

For the next steps, Reclamation will investigate a range of reservoir release strategies, focusing on temperature and flow velocity combinations. These studies will determine the most effective ways to disrupt the spawning habits of smallmouth bass.

Additionally, the Notice of Intent for a Supplemental Environmental Impact Statement and an amended Record of Decision for the 2016 Long Term Experimental and Management Plan has been released. The public is encouraged to share their thoughts on the operational guidelines, potential impacts, and any other concerns.

Reclamation will be hosting two public webinars to offer more details and gather oral comments. The Notice of Intent will be available for public comments for 30 days after its publication in the Federal Register.

Further information:  Glen Canyon Dam Adaptive Management Program webpage.

Image:  Glen Canyon Dam via Bureau of Reclamation press release.