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Backwater habitats aze formed b the c cle of sediment d osition durin eak flows and Y Y eP g p subsequent scouring processes during and after peak flows. In a study of backwater availability and flow regulation, Pucherelli and Clazk (1989) found that backwater availability increased through the summer as flows decreased. A gradually decreasing hydrograph was required to maximize availability, but they speculated that high spring flows may be necessary to establish the proper sediment conditions. Stanford (1994) noted that the relationship developed by Pucherelli et al. (1990) for a single year's topography would only be valid for that yeaz, and would likely change in subsequent years as the channel morphology changed in response to flood peaks. Habitat availability at base flow is a product of channel morphology. Within-channel morphology in this dynamic system may vary greatly from yeaz to yeaz. Thus, annual variability in habitat availability is expected. Further study was needed to determine the geomorphic processes which form, maintain and maximize total and quality nursery habitat. The biological response of Colorado pikeminnow and sympatric species to changes in flow and habitat availability also needed to be assessed. The Interagency Standardized Monitoring Program (ISMP) includes yeazly monitoring of young-of--year (YOY) pikeminnow by seining backwaters in the fall. Reseazch leading up to the establishment of the ISMP suggested that young pikeminnow preferred lazge, deep backwater habitats with temperatures higher than the main channel (Tyus et al. 1982; Valdez et al. 1982; Archer et al. 1985). During the first five years of the ISMP and during other studies, high variation in catch rates was observed within these habitats, suggesting a need to further refine the definition of quality nursery habitat (McAda et al 1992), as well as the sampling protocols. OBJECTIVES Th ere were ten objectives listed in the scope of work proposal for this project. Objective 1 was addressed jointly by the Utah Division of Wildlife Resources (UDWR) and the Geography Department at Utah State University (LTSU). In addition, objectives 2-3 were addressed by USU and all aze reported in Chapter 1. That portion of the study concentrated on how the river system creates and maintains certain types of habitats and how flows can be manipulated to maximize habitat favorable to YOY pikeminnow in the Ouray azea of the Green River (Reach 2). Objectives 4-10 were addressed by the Utah Division of Wildlife Resources. These objectives focus on the biological response of Colorado pikeminnow and sympatric species to changes in flow and habitat. The Ouray reach (Reach 2) is reported in Chapter 2, and the Mineral Bottom reach (Reach 3) is reported in Chapter 3. Chapter 4 details the evaluation of sampling efficiency in this and other studies in the Recovery Program. The objectives were: 1) Determine the relationship between availability, formation, and maintenance of Colorado pikeminnow nursery habitat and test release flows from Flaming Gorge Dam. 2) Develop defmitions for habitat types based on fluvial geomorphological processes. 3) Describe the relationship between geomorphological processes of sediment transport and nursery habitat formation and maintenance in the Green River.