Thursday June 5, 2025
Bureau of Reclamation —
The Bureau of Reclamation and the National Park Service have completed modifications to a warmwater slough in the Colorado River near Glen Canyon Dam removing a key spawning site for invasive smallmouth bass—a growing threat to native fish.
Located 3.5 river miles downstream from the dam and 12 river miles upstream from Lees Ferry, Arizona, the shallow slough within the Glen Canyon National Recreation Area had become a hotspot for warmwater, nonnative fish due to its elevated temperatures. The project involved reshaping the slough to increase water flow and reduce temperatures, creating unfavorable spawning conditions for smallmouth bass and other invasive species.
“The establishment of warmwater nonnative predatory fish—particularly smallmouth bass—in the Colorado River below Glen Canyon Dam is an imminent threat to the recovery of the humpback chub, a federally protected, threatened species,” said Wayne Pullan, Reclamation Upper Colorado Basin Regional Director. “This channelization effort demonstrates the power of partnerships and adaptive management in protecting the Colorado River ecosystem.”