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EXECUTIVE SUMMARY The purpose of this study was to inventory all potential flooded bottomland habitats in the Upper Colorado River Basin that were believed to be important for recovery of endangered fishes, especially razorback sucker, and rank (prioritize) the bottomland sites. All potential bottomland habitats adjacent to stream reaches in the Upper Colorado River Basin (871 river miles) that were considered important for recovery of endangered fishes were inventoried in 1993. A total of 293 bottomland habitat sites in the Green River (135 sites) and Colorado River (158) drainages was identified, categorized, and classified using a five-step procedure to objectively prioritize bottomland sites. Each site was scored and prioritized (ranked) from four selection criteria (land ownership, proximity to a known or planned razorback sucker spawning area or proximity to recent adult captures, June hydrological connection to the river, and potential for a network [complex] of bottomland sites) that were based on available photographic imagery and the most current biological information. Prioritizing the bottomland sites was also used to establish staff gauge and river transect locations in 1994 to determine flows necessary to inundate a specific bottomland site. In the Green River drainage, the largest flooded bottomland areas were located in the Browns Park National Wildlife Refuge reach (1,371 acres [555 ha]) and between Escalante Ranch and Pariette Draw (6,093 acres [2,466 ha]). The greatest concentration of flooded bottomland sites were within the Ouray National Wildlife Refuge (2,265 acres [917 ha]). In the Colorado River drainage, there were three distinct areas where bottomland habitats were concentrated. These were usually in large floodplain areas near agricultural centers. The first area was the stream reach between Rifle and Debeque, Colorado (2,248 acres [910 ha]), the second was the stream reach in the Grand Valley between Palisade and Loma, Colorado (4,564 acres [1,847 ha]), and the third area between the Cisco Boat Landing and McGraw and Hotel Bottoms (1,214 acres [491 ha]) upstream from Moab, Utah. Moab Slough, near Moab, Utah, was the largest, single bottomland area along the Colorado River encompassing approximately 875 acres (354 ha). In the Gunnison River drainage, the largest and only major floodplain area was between Austin, Colorado, and Roubideau Creek (1,739 acres [704 ha]; 17 river miles [27 rkm]). The average inundated area during both the May and June runoff and the low-flow period in September was larger in the Green River (May and'June: mean = 59 acres [24 ha]; September: mean = 19 acres [8 ha]) than any of the sites inundated in both the Colorado River (May and June: mean = 22 acres [9 ha]; September: mean = 10 acres [4 ha]) or Gunnison River (May and June: mean = 17 acres [7 ha]; September: mean = 3 acres [1 ha]). In the Green River, the bottomland habitat sites between Pariette Draw and Escalante Ranch (32 sites) were ranked 1 through 11. Bottomland habitat in the Ouray National Wildlife Refuge (six sites) were the highest ranked (1st and 2nd) sites. The Browns Park National Wildlife Refuge (eight sites) sites ranked (12th-14th) the next highest, followed by lower ranked (17th-18th) sites from Pariette Draw to the Green and Colorado river confluence (92 sites). Based on these rankings, there were five general bottomland habitat xiii