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I. PURPOSE AND NEED A. General. The Colorado River and its tributaries provide water for municipal use, irrigated agriculture, industry, and mining (Bishop 1971). Bishop emphasizes that these various uses of water have resulted in conflicts. Water development in the Upper Colorado' River Basin altered the natural river ecosystem (Miller et ale 1982; Wydoski 1980). Dam construction and storage of water to serve human needs changed the natural hydrograph through dam operations that released water for the irrigation season (Johnson 1974) or for generating power during peak use periods. Changes in the hydrograph have, in turn, altered aquatic habitats, particularly backwater and floodplain habitats that are vital to the early life stages of native fi shes. Co 1 dwater releases from dams have reduced water temperatures of the natural and historic warmwater aquatic ecosystem. Water quality has been impacted from toxic heavy metals through mining activities and from increased selenium concentrations through irrigated agriculture. Nonnative fish species were introduced in the rivers and ~anmade reservoirs, both Intent i ona 1 and accidental i ntroduct ions of nonnative fi sh speci es have changed the composition of the natural fish community. Human alteration of the Upper Colorado River Basin (Figure 1) has resulted in four endemic fishes (razorback sucker, Xvrauchen texanus; bony tail, Gila eleqans; humpback chub, Gila ~; and Colorado squawfish, Ptvchocheilus lucius) being listed as lIendangered" under the Endangered Species Act. Although numerous factors have contributed to listing these native fishes as endangered, several factors appear to be particularly important. Habitat alteration and introduction of nonnative fish species were considered to be the most important factors in the extinction of 40 native North American fishes (27 species and 13 subspecies) during the past century (Miller et ale 1989) . These two factors undoubtedly contri buted to the demi se of the endangered Colorado River fishes. B. Purpose. Endangered fishes in the Upper Colorado River Basin have been and continue to be impacted by a number of factors including water depletions, disrupted natural hydrograph through the operation of dams for irrigation and hydro-power, losses of riverine backwaters and floodplain habitat from altered streamflows, barriers to native fish migration, and predation by and competition from nonnative fish species. Various recovery actions have been taken to resolve water depletions, streamflow patterns, migration barriers to fish by dams, and rehabilitation or restoration of floodplain habitat. In 1996, the Recovery Implementation Program for Endangered Fishes in the Upper Colorado River Basin (Recovery Program) developed a strategic plan to control nonnative fi sh speci es. Recovery Program part i ci pants, representing various interests, were directly involved in the development of the strategic plan to control nonnative fish species that is summarized by Tyus and Saunders (1996). Nonnative fishes compose 76% of the fish species (42 of 55 species) in the riverine enVironment of the Upper Colorado River Basin (Tyus et ale 1982). These nonnative fishes constitute most of the fish numbers (96.7 - 99.6%) found in backwater habitats in the Upper Basin (Cranney 1994; McAda et ale 1