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to predation and competition by nonnative fishes that compose 76.4% of species in the present fish community (Tyus et al. 1982) and starvation (Marsh and Langhorst 1988). Since the density of zooplankton in the main channels and backwaters in the Upper Colorado River Basin are not sufficient to maintain razorback sucker during the critical early life period (Figures 1 and 2; Tables 1 and 2), it is reasonable to assume that competition from nonnative fish species a 1 so contri butes to starvation and subsequent mortal i ty of endangered fi sh larvae. Reconnecting the floodplain with upper basin rivers will enhance or restore the natural function of the riverine ecosystem. XII. STRATEGIES TO ENHANCE OR RESTORE FLOODED BOTTOMLAND HABITATS IN THE UPPER COLORADO RIVER BASIN The bas i c ecol ogi ca 1 requi rements of space, water qual ity, streamflow, cover, and food must be reviewed by life stage in recovery efforts since all are important in maintaining self-sustaining populations. Quantity of water (height of the flood) and timing that are important to fish reproduction must be based on an adequate knowledge of riverine fish species (Welcomme 1985). The larval fish of many species in large rivers drift downstream, move laterally onto the floodplain during high streamflows, return to the main channel as the floods subside, and move upstream as they become larger (Welcomme 1985). Secondary channels and backwaters, that remain connected to main ri ver channels, have many characteristics of floodplain habitats (i.e., shallow, clear, and warm) and are more productive than the main channel (Welcomme 1985). Razorback sucker adults are flexible in their use of habitats. Although this species evolved in large riverine systems, adults have survived well in both lacustrine (Wallis 1951, Marsh and Langhorst 1988) and lotic (Tyus 1987) habitats. Razorback suckers may spawn in lotic environments (Tyus and Karp 1990) or in lentic environments (Minckley et al. 1991). However, it has been suggested that early life history stages require inundated floodplains to grow and survive (Tyus and Karp 1989, 1990, 1991). Rapid growth of razorback sucker juveniles in off-channel habitats was reported by Osmundson and Kaeding (1989a) and Mueller et al. (1993a). The use of fl oodp 1 a ins for agri culture, hous i ng, and i ndust ri a 1 uses has increased in demand and these uses have increased river pollution (Welcomme 1985). Fish assemblages in large rivers vary considerably and are often related to the connectivity of the floodplain with the main channel (Copp 1989). During low streamflows, backwater habitats become important in sustaining fish populations. Some fish species have modified their behavior to use backwaters and secondary channels of large rivers as substitutes for floodplain habitats as nurseri es (Weclomme 1995). Species that cannot adapt to the ri veri ne envi ronment when floodplain habitats are no longer available will perish. The restoration of large floodplain rivers will require at least partial recovery of the natural hydrograph based on the current knowledge of such systems (Bayley 1991; Hesse 1995; Ward and Stanford 1995). It is believed that natural lateral expansion of the floodplain and river-basin management are perhaps the best methods of flood control because of the growing awareness of inadequacies of structural measures to control floods (Welcomme 1985). Dolan et al. (1974) stated that the historic natural state of Colorado River System can no longer be 12