The Glen Canyon Dam Temperature Control Device: Restoring Downstream Habitat for Endangered Fish Recovery

Prior to closure of Glen Canyon Dam in 1963, the temperature of water flowing down the Grand Canyon each year varied from near freezing to 30°C during the heat of summer. Since construction of the dam, cold water (7 to 10°C) has been released from the deeper levels of the reservoir. For several miles below the dam, these cold water releases have created an excellent tailwater trout fishery. But as the water flows downstream through the Grand Canyon, it only warms to about 15°C which is not warm enough to allow endangered native fish species, like the humpback chub (Gila cypha), to reproduce and thrive in the Colorado River. Researchers believe that increasing the water temperature from Glen Canyon Dam is an important component in restoring habitat for the humpback chub and other native fish in the Grand Canyon. However, biologists fear that increasing river temperatures may encourage nonnative warm water fishes to move up the Grand Canyon or stimulate parasites or other disease agents that are currently controlled by colder water. A TCD (temperature control device) retrofit to Glen Canyon Dam would allow operators to adjust release water temperatures to improve habitat and to minimize potential negative impacts of cold water releases. The decision to construct a TCD will involve considering the potential that warm water releases will create unacceptable levels of competition or predation by nonnative fishes, the introduction of diseases or parasites that could negatively impact the humpback chub or other species of concern. Currently, the risk versus reward of adding selective withdrawal capability to Glen Canyon Dam is being evaluated by the Glen Canyon Dam Adaptive Management Program, regulatory agencies and stakeholders.