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Snyder 1995). Slightly over 3% of 53,750 larval or early juvenile fish captured in the middle Green River during 1992-1996 were razorback suckers and less than 1% of 59,220 larval and early juvenile fish in the lower Green River were razorback suckers (Muth et al. 1998). Nonnative cyprinids (red shiner, sand shiner Notroois stramineus, carp Cvorinus carpio, and fathead minnow dominated the total light trap catch during 1993 (88%) and 1995 (70%) and native catostomids (bluehead and flannelmouth suckers) dominated the light trap catches in 1994 (97%) and 1996 (63%) in the middle Green River (Muth et al. 1998). Muth et al. (1998) stated that "Annual initiation of razorback sucker spawning in the Green River during our investigation [1992-1996] was probably triggered by a suite of interacting environmental cues that could not be detected in our analysis of individual water temperature and discharge parameters." The high percentage of nonnative cyprinids in certain years (such as 1993 and 1995) could be significant competitors with razorback sucker larvae because food resources are limited in the main channel and backwaters of the middle Green River. I I I J A field experiment in backwaters of the middle Green River with complete, partial, or no fish exclosures demonstrated that fish can significantly reduce planktonic and benthic food resources and that diet overlap by nonnative fishes could result in competition with native fishes (Collins and Shiozawa 1994). These findings are consistent with results from studies on smaller streams where invertebrates in low velocity habitats with soft substrates have been reduced by fish predation (Angermeier 1985; Gilliam et al. 1989; Schlosser and Ebel 1989). Similar studies of large rivers were not found in the literature. V. IMPORTANT FLOODPLAIN HABITATS IN THE UPPER COLORADO RIVER BASIN Floodplain habitat sites (135 sites in the Green River Subbasin [Green River - 132 sites; potential area of 7,458 ha or 18,430 ac, Yampa River - 1 site; potential area of 8.9 ha or 21 ac, and White River - 2 sites; potential area of 256 ha or 634 ac) and 158 sites in the Colorado River Subbasin [Colorado River -110 sites; potential area of 4,948 ha or 12,222 ac] and Gunnison River - 48 sites; potential area of 1,305 ha or 3,223 ac) that could provide nursery areas for recovery of the razorback sucker and perhaps other endangered fishes were inventoried and classified during 1993 (Irving and Burdick 1995) . I 1 t ,I - I 1 A. Green River Subbasin. Most floodplain habitat sites along the Green River are located between pariette Draw upstream to Escalante Ranch (Irving and Burdick 1995; RK 383-499 (RM 238-310]; 2,466 ha [6,093 acres)). Floodplain terraces comprised the vast majority (75% of 99) of habitat in the Green River Subbasin while floodplain depressions comprised the remaining 25% of sites. Four percent of the 132 potential floodplain sites along the Green River were separated from the river by natural levees while 11% were separated by levees constructed by humans. Approximately 32 km (20 mil of the Green River consisted of natural and human-constructed levees at 20 sites. In early 1998, floodplain areas were evaluated based on three criteria: (1) Biological importance to the endangered fishes.; (2) Opportunities for floodplain enhancement/restoration.; and (3) Focus on areas that flood or could be made to flood under present streamflows (P. Nelson, 1998, personal communication). In the Green River Subbasin, high priority reaches included RK 185 to RK 212 (RM 115 to RM 132 [Green River, Utah)) and RK 383 (RM 238; pariette Draw) to RK 515 (RM 320; Dinosaur National Monument) . 26 II , I I B. Colorado River Subbasin. Most floodplain habitats along the Colorado and Gunnison rivers were scattered in four general areas (Irving and Burdick 1995): (1) Colorado River between Debeque and Rifle, Colorado (RK 327-386 I