How might threatened and endangered species be affected by dam operations?
Damming the Colorado River has changed the way water courses and pulses through Grand Canyon. Much of the sediment that the river naturally carries is trapped behind Glen Canyon Dam. Water released from the dam is colder than historical temperatures. Reduced temperatures changed the prey base available to native fishes and altered their spawning productivity and survival in the mainstem river while it favored cold water non-natives that prey upon and compete with native fishes. Daily water level fluctuations below the dam inundated and dried near-shore habitat that supported native fishes and the Kanab ambersnail. Reduced sediment loads interrupted the rejuvenation of warm, still backwater habitat and depleted beaches needed for the growth of riverside riparian vegetation. Attenuation of seasonal flood cycles altered the hydrological cleansing and rejuvenation needed to sustain native riparian habitat essential to southwestern willow flycatcher nesting.
