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These enhancement activities provide the mechanisms for reconnecting lowland areas to the ri ver and i ncreas i ng the durat i on of i nundat i on in off-channel habitats. Since peak spring streamflows are lower and the connection of the floodplain with the river has been reduced, habitat enhancement or restoration will result in higher production of zooplankton that is required by larval razorback suckers. Ideally, reconnecting the floodplain habitat with the main river channels should simulate natural conditions where possible and be relatively maintenance free. In practice, however, human intervention will be required to control nonnative, warmwater fishes that are expected to thrive in enhanced or restored floodplain habitats and that are estab 1 i shed in backwaters in the Upper Colorado River Basin. In addition, increasing spring streamflows to flood lowland habitats will result in sociological problems associated with flooding private, agricultural land and production of mosquitoes that could pose human health problems. XIII. INTEGRATION OF HABITAT ENHANCEMENT OR RESTORATION WITH CONTROL OF NONNATIVE FISHES AND CAPTIVE PROPAGATION Adequate Nonnative Fish Control is Essential for Survival of Razorback Sucker Larvae. If control of the nonnative minnows, green sunfish, small mouth bass, and juvenile largemouth bass is possible in the general vicinities of enhanced or restored flooded bottoml and habi tats (part i cul arly downstream), razorback suckers may develop self-sustaining populations. However, the size attained by razorback suckers is only about 25 mm TL in 8 weeks (Figures 1 and 2). The body of a 25 mm razorback sucker is deep and wide enough to preclude predation by adult red shiner based on the gape size of red shiner mouths (T. Crowl, 1995, Personal Communication). A razorback sucker of 25 mm would still be prey for fathead minnows since these minnows tear their prey apart and feed on the pieces (Dunsmoor 1993). In addition, razorback larvae of 25 mm as well as juveniles would still be highly vulnerable to predation by green sunfish, smallmouth bass, and juvenile largemouth bass. Enhancement of bottoml and habi tats shoul d help to provi de adequate food resources that will, in turn, increase survival of larval and juvenile endangered fishes. However, such off-channel, low velocity, warmwater habitats are also ideal for nonnative fish species that may prey upon or compete with early life stages of the endangered fishes. Recovery of the endangered fishes will be dependent on sufficient survival of larvae and juveniles that will provide adequate recruitment to maintain self-sustaining populations. Total control of the nonnative fishes is not possible in the Upper Colorado River Basin (Wiley and Wydoski 1993) because these fishes are well established with self-sustaining populations. If partial control using mechanical control methods (e.g., removal with various gear, increased water velocity, etc.) does not remove an adequate proportion of the nonnative fi sh popul at ion, then compensatory mechanisms of increased growth and fecundity will allow rapid repopulation by nonnative fishes. Experimental partial control of nonnative fishes should be evaluated in river reaches where experimental floodplain enhancement or restoration is completed to benefit the early life stages of the razorback sucker. All habitat enhancement or restoration endeavors and nonnative fish 15