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pikeminnow reproductive success. Reproductive success of razorback sucker was not monitored in the Colorado River, but successful reproduction in the Green River was associated with flows sufficient to inundate floodplains and provide warm, food-rich environments for growth and survival of larval fish. Successful reproduction of these species was associated with flows sufficient to clean cobble bars of fine sediments and provide sediment-free interstitial spaces for incubation of eggs. Increased volume of interstitial spaces was also associated with increased primary and secondary production in the Colorado and Gunnison rivers. Abundance of three nonnative cyprinids (fathead minnow Pimephales promelas, red shiner Cyprinella lutrensis, sand shiner Notropis stramineus) was reduced in years with higher than average spring runoff. These three species are very abundant in some reaches and may prey on or compete with young of the endangered fishes, especially Colorado pikeminnow. Reduced abundance was temporary, but it may have reduced predation or competition and allowed for increased survival of young Colorado pikeminnow in some years. The endangered fishes use a variety of habitats depending on season and species. Adult Colorado pikeminnow and razorback sucker prefer braided reaches that offer a suite of habitats in proximity to one another. Humpback chub are restricted to canyon-bound reaches and used eddies and pools during most of the year. Inundated floodplains provide warm, food-rich environments for adult Colorado pikeminnow and razorback sucker in addition to being critical for survival of larval razorback sucker. Young-of-the-year (YOY) Colorado pikeminnow are dependent o.n backwaters in the lower Colorado River for nursery habitat. Movement of fine sediment through the Colorado and Gunnison rivers is critical to creation and maintenance of endangered-fish habitat. Flows equal to or greater than 1/2 bankfull discharge carry 65-75% of the sediment load of the Colorado and Gunnison.rivers. Flows. equal to_ or greater.than bankfull discharge create and maintain in-channel features such as pools or side channels and provide inundated floodplains. Bankfull discharge also moves sediments to create and maintain backwaters, but low, stables flows are necessary to make backwaters available to YOY Colorado pikeminnow following the summer spawning period. Overall, a more naturally shaped hydrograph is necessary to create and maintain habitats for the endangered fishes and to provide needed habitats at the correct time. Flow recommendations for the Colorado and Gunnison rivers were developed using a lines-of-evidence approach similar to that used to develop flow recommendations for the Green River (Muth et al. 2000). Specific relationships between biological response and river flow were used to quantify, the underlying cause for the biological response; e.g., sediment transport that improved hatching success or increased primary production. Flows that create and maintain riverine habitats that are critical to the endangered fishes (e.g., backwaters or floodplains) were also considered in developing the recommendations. The fundamental basis of flow recommendations for the Colorado and Gunnison rivers reflect general guidelines for river restoration proposed by experts in the field; partial restoration of natural functions that benefit the riverine ecosystem were hypothesized to benefit the endangered fishes as. well. The goal of these recommendations is to provide the annual and seasonal patterns of flow in the Gunnison River and in the Colorado River downstream from their confluence to Final Report xx July 2003