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depressions that are currently not connected to the river and receive water from groundwater infiltration, wetland terraces that are only inundated during flooded periods, or canyon mouths that are "ribbon-like" channels in narrow canyons adjacent to the main river flow. During high flow events, some of these off-channel features are temporarily connected to the river. Re- establishing connectivity to the mainstem river may provide off-channel habitats for endangered fishes that are essential for effective management of the riverine ecosystem and recovery of endangered fishes. Former natural riverine features could be integrated into the historic floodplain by removing portions of human-made dikes or natural obstructions (e.g., gravel and sand bars). Habitat development and enhancement is identified as one of the five principal elements of the Recovery Program (U. S. Fish and Wildlife Service [FWS] 1987). Protection, restoration, and enhancement of inundated bottomland habitat along mainstem riparian corridors are believed to be important for recovery of razorback sucker. Riparian enhancement in the Upper Colorado River Basin can be accomplished by providing sufficient flows to inundate bottomlands in a manner that approximates the natural hydrograph. If sufficient flows cannot be obtained regularly, dikes and levees should be breached at intervals to allow inundation of lowlands during high spring flows. Restoration of flooded bottomland habitats will provide food that should increase survival of larvae and juveniles of endangered fishes as well as provide resting and feeding areas for adults. Before razorback sucker are reintroduced into historical stream reaches of the Upper Colorado and Gunniso,d\ rivers, a habitat enhancement program (i. e., flooded bottomland management) must be implemented if recovery is to be realized. Purpose and Objectives The purpose of this study was to summarize 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. The inventory of these habitats provides managers with candidate sites for acquisition, restoration, and management. The objectives of the study were to: 1. Identify bottomlands adjacent to Upper Colorado River Basin mainstem rivers representing potential endangered fish habitat. 2. Categorize and classify the bottomlands identified according to potential value for endangered fish recovery. 3. Rank (prioritize) mainstem bottomlands by their perceived value to endangered fish recovery. The end product is an inventory of mainstem flooded bottomlands categorized by size (area), extent of flooding, fish and water access, upland vegetation types, ownership, and related criteria. Sites were ranked as to potential contribution to endangered fish recovery. 2