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juvenile razorback sucker (Taba et al. 1965, Gutermuth et al. 1994, Robert Muth Personal Communication, in Modde 1996) have been documented in the Upper Colorado River Basin since the completion of Glen Canyon Dam. All of these fish were collected in backwaters. Based on documentation that adults use floodplain habitats (Tyus and Karp 1990, 1991) and circumstantial evidence that floodplains are important nursery habitats for age-O razorback sucker, the Recovery Implementation Program initiated a demonstration project to describe nursery suitability and fish use in a floodplain depression wetland. The goal of this study was to determine whether floodplain wetlands were used by age-O razorback sucker, and if so, propose strategies to manage these habitats to recover this species. The approach taken was to describe the nursery suitability of Old Charley Wash for razorback sucker, and describe the dynamics of fish use in Old Charley Wash during the spring and summer months. The unique water control structure at Old Charley Wash also enabled a fish census to compare fish collections with the true composition of the floodplain wetland. Using the above approach, the specific objectives of the study included: 1) determine if water quality and prey (Le. zooplankton) densities existed in Old Charley Wash to support age-O and razorback sucker through the summer months, 2) describe the composition, temporal occurrence, and habitat use of fishes in Old Charley Wash, and 3) integrate information from this study with existing knowledge to recommend management actions that will enhance recovery of razorback sucker. Study Area The study was conducted at Old Charley Wash (also known as Wood's Bottom), a 147 ha floodplain wetland on the Ouray National Wildlife Refuge near Ouray, Utah (Figure 1). The wetland is subdivided into two units (main and backside units). Water entered Old Charley Wash through an inlet canal (via gravity flow) connected to the Green River when flows reach 240 m3/s, and the protective dikes were inundated by the Green River at approximately 396 m3/s. Throughout the study a grate structure with bars spaced 12.7 mm apart was placed over the inlet canal to prevent access by larger fish. Only the main unit (80 ha) was evaluated in this study (the backside unit receives overflow water from the main unit via a stop-log structure). The main unit of Old Charley Wash has a regular, bowl-shaped bottom profile. The primary vegetation in the wetland is smart weed Polygonum sp. sago pond weed Potamogeton pectinatus and small quantities of bulrush Scirpus sp. and cattail Typha sp. are also present around the periphery of the wetland. Between 1993 and 1996 Old Charley Wash was drained prior to the winter months and filled the following spring with flood flows. The outlet water control structure was closed in the spring each year to allow retention of water in the wetland and was only opened when the wetland was drained. In 1993, the original outlet dike was modified by adding a screw-gate water control structure and the drainage canal was graded to the deepest portion of the wetland to allow complete draining of the wetland. Because of the difficulty in harvesting fish from the drainage canal in 1994, the outlet structure was further modified in 1995. The modified structure included a smaller second dike constructed approximately 12 m up the drainage canal from the original outlet dike. Both dikes were equipped with screw-gate water control valves. The floor of the drainage canal between the primary and secondary dikes was lined with concrete and the canal sides were lined with a polyethylene cellular material filled with gravel. The modified outlet 10