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EXECUTIVE SUMMARY Warm, quiescent, backwater habitats are critical nursery areas for some warm- water fishes native to the upper Colorado River. Today, non-native fishes numerically dominate fish assemblages within upper Colorado River backwaters and their interaction with young of Colorado pikeminnow Ptychocheilus lucius and razorback sucker Xyrauchen texanus may be important impediments to recruitment of these endangered species. Largemouth bass Micropterus salmoides and green sunfish Lepomis cyanella are the most common, large-bodied, non-native, piscivorous fish species that inhabit upper Colorado River backwaters year-round. Young-of-the-year (YOY) and yearling- sized Colorado pikeminnow are highly susceptible to predation by these introduced centrarchids. As part of recovery efforts for the endangered fishes, mechanical removal of centrarchids from upper Colorado River backwaters was undertaken in an attempt to reduce potential predation. The primary objective of this three-year project was to remove from backwaters all centrarchids and other large, nonnative fish species deemed detrimental to the native fish community. A secondary objective was to evaluate efficacy (both practicality and degree of measurable success) of using mechanical removal of predators as an ongoing recovery program activity. The ultimate goal of non-native fish removal is to increase survival rate of larval and juvenile endangered fish. Backwaters were electrofished twice annually from 1999 through 2001: once prior to spring runoff (March-April) and once following runoff (August-October). Each season, one pass was made through the target reach with an electrofishing boat, followed by a second pass using an electrofishing barge. Together, these two methods shocked a total of 30-48 separate backwaters per season. During the three-year effort, 3,758 largemouth bass, 10,432 green sunfish and 630 bluegill Lepomis macrochirus were removed. Other abundant nonnative fish removed included 6,642 common carp Cyprinus carpio, 3,551 black bullhead Ictaluras melas, and 2,807 white sucker Catostomus commersoni. Additional non-native species included channel catfish Ictaluras punctatus, black crappie Pomoxis nigromaculatus, smallmouth bass iv