Abstract

Of all the major dams on the Colorado River system, advocates of dam decommissioning have focused their attention on Glen Canyon Dam. Among the arguments offered in support of this decomissioning is restoration of the Colorado River biological systems in Glen and Grand Canyons both upstream and downstream of the dam. Specific mention has been made of the benefits that theoretically would accrue to endangered species in and along the river, particularly native fish species. The purpose of this paper is to: (1) identify ecological components that likely would be affected by removing or bypassing Glen Canyon Dam; (2) speculate (given the sketchy nature of available data) on how such action might affect endangered species, particularly native fish; and (3) take a broader, albeit less visionary, look at managing a regulated Colorado River system for endangered species. We focus our discussion on endangered species because of the power of the Endangered Species Act of 1973 ("ESA") to shape natural resource management actions.

Four primary difficulties complicate any attempt to determine the influence of reservoir drainage on biological systems upstream and downstream of Glen Canyon Dam. First, the terrestrial and aquatic ecosystems of Glen and Grand Canyons were only cursorily studied before the dam was built, rendering our assessment of the dam's impacts somewhat speculative; second, by the late 1800s the pre-dam river's ecosystem had already been altered by the introduction of nonnative species, especially several fish species known to be competitors/predators of the native fish; third, after almost forty years of dam operations, the dynamic nature of the post-dam river in Grand Canyon has not yet reached equilibrium; and, fourth, in the absence of rigorous data collection and analysis, any assessment of how the floral and faunal elements would respond to a drained lake must be, by definition, speculative.

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