Back in February, USGS WFRC science technician, Georgia Martin, and fish biologist, Collin Smith, took a trip to Glen Canyon Dam (GCD) as a part of an upcoming study slated to begin in early 2025. In the photograph, they are pictured evaluating the study location, retrieving nets and checking for juvenile fish samples to determine the proper net mesh size for the study. The 2024 tailrace sampling pilot study was conducted to assess gear and deployment methods, aimed at capturing fish that pass from the forebay through the turbine outlets and enter the tailrace below the dam.

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Invasive fish recently captured in the Colorado River downstream of GCD indicate a potential threat to imperiled native fish in the Grand Canyon. Within the last two years, biological survey teams have observed increasing captures of invasive fish species including smallmouth bass, green sunfish, and bluegill throughout the Lees Ferry Reach (approximately 15 river miles from GCD). Observations of these warmwater species downstream of GCD were previously uncommon, but decreasing reservoir elevations in Lake Powell (the reservoir created by GCD) are hypothesized to increase the passage of invasive fish (entrainment) through the dam. The establishment of functional reproducing populations of non-native fish downstream of GCD will likely result in adverse effects on native fish populations within the Grand Canyon section of the Colorado River through direct predation or competition for resources. 

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WFRC scientists are frequently called upon nationally for their unbiased, scientific expertise in fish passage solutions. In this case, our partners at the USGS Grand Canyon Monitoring and Research Center and the Bureau of Reclamation requested our support.

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