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INTRODUCTION Background Historically, Upper Colorado River Basin floodplains were inundated more frequently by flows during spring runoff, but today floodplains are not regularly connected to the river because of channelization by either levees and dikes or rip-rap near population centers in agricultural areas. Introduced salt cedar or tamarisk (Tamarisk spp.) has become established along the shoreline of major rivers resulting in sediment deposition and stabilized banks that further reduce the connectivity of the river with historic flooded bottomlands (Graf 1978). The periodicity of out-of-channel floods-ng in the Upper Colorado River has dramatically decreased following the onset of transmountain water diversions, irrigation diversions, and the construction of mainstem dams (Osmundson and Kaeding 1991). The construction of dikes coupled with the reduction of high spring flows has altered the natural hydrograph and either reduced or eliminated regular flooding of bottomlands. It is believed that flooded bottomlands may have served as nursery areas for the razorback sucker Xyrauchen texanus (McAda 1977; Osmundson and Kaed'ing 1991). In addition, Osmundson and Kaeding (1991) suggested that oxbow lakes and flooded pastures in the Grand Valley near Grand Junction, Colorado, were historically the primary spawning habitats of the razorback sucker. They also suggested that low-velocity, off-channel habitats were used by adult Colorado squawfish (Ptychochei7us 7ucius) during high stream flows. Numerous studies (Grabowski and Hiebert 1989; Tyus and Karp 1989; Wydoski and Wick 1994) have suggested the importance of seasonal flooding to river productivity. Flooded bottomland habitats were considered important to adult razorback sucker for feeding prior to and after spawning and also important as nursery areas (Tyus and Karp 1989). Adult fish may have used these off-channel habitats for "velocity shelters" to escape high water velocities during spring runoff. Turbid rivers in the upper basin are not very productive for zooplankton that are essential food for early life stages of razorback sucker. When compared to the riverine environment and river backwaters, inundated bottomland habitats produce the higher densities of zooplankton (Grabowski and Hiebert 1989; Mabey and Shiozawa 1993). Although predation by non-native fishes has been documented to be a limiting factor in survival of larval razorback sucker in the lower basin (Minckley et al. 1991), starvation may also limit survival (Marsh and Langhorst 1988; Papoulias and Minckley 1990). It is hypothesized that the loss of these productive flooded bottomland habitats is limiting recruitment of razorback sucker in the Upper Colorado River Basin because of insufficient quantity of appropriate-sized food organisms at the right time (Wydoski and Wick 1994). Most flooded bottomland habitats occur in broad valleys along low- gradient stream reaches. Bottomlands are off- or out-of-channel habitats that include oxbow lakes, former side channels in broad valley floodplains, ponds, and wetland depressions and terraces. Less numerous flooded bottomland habitats are found in canyon-bound stream reaches. These are wetland