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juvenile native fish in upper Colorado River backwaters is probably from largemouth bass followed by green sunfish and black bullhead. Although introduced red shiners, an abundant member of many upper Colorado River backwater communities, are capable of preying on larval native fishes (Ruppert et al. 1993), native fishes quickly grow out of the size range vulnerable to predation from these small minnows. However, the common occurrence of largemouth bass, many as large as 175 mm long, greatly extends the window of predation vulnerability for Colorado pikeminnow and other native fishes, including larvae, YOY and yearling-size individuals. Although green sunfish are perhaps not as piscivorous as largemouth bass, their abundance and widespread distribution make them a significant threat to native fish survival in backwaters. Experiments in pond- stocking of Colorado pikeminnow revealed that green sunfish can consume pikeminnow 60% of their own length (Osmundson 1987). In electrofishing efforts reported here, 20% of green sunfish in backwaters were 100-150 mm long, and hence capable of preying on Colorado pikeminnow 60-90 mm long. Although barge-shocking proved the most effective means to mechanically remove centrarchids from backwaters, non-natives were only partially removed from individual sites and no reach-wide depletive effect was demonstrated after six seasonal removal efforts. Total cost for the field effort was $156,000, which translates to a cost of $10.49 for each centrarchid removed. When all non-native fish are considered, the cost of removal was about $5.58 per fish. Other means to reduce centrarchids should be explored, including better techniques to physically remove individuals from particular sites as well as management strategies that keep backwaters from developing pond-like conditions that allow centrarchids to thrive. In certain cases, chemical treatment of seasonally-isolated backwaters might be accomplished with little risk to native fish. This may prove a more thorough means to eradicate non-native fish from some high-concentration sites than did electrofishing. In addition to irrigation returns, these floodplain `hotspots' may be important sources of centrarchids present in other backwaters. Probably the most effective means to reduce or eliminate a species is to destroy its habitat. The relationship between sustained periods of low river flow and enhancement of centrarchid habitat in 23