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Final Report September 2000 Differences in mean daily flows between consecutive days caused by reservoir operations should not exceed 3%. Flow variations resulting from hydropower generation at Flaming Gorge Dam should be limited to produce stage changes of no more than 0.1 m within a day at the U.S. Geological Survey (USGS) gage near Jensen, Utah. Wet (0-10% exceedance) and moderately wet (10-30% exceedance) years were identified as being critical for razorback sucker recruitment in Reach 2 because the recommended peak flows in those years would be high enough to provide the substantial floodplain inundation that is critical to the growth and survival of larval and age-O fish. Inundation of floodplain habitats would also provide growth and conditioning habitats for other species and restore certain ecosystem functions dependent on river-floodplain connections. Although Colorado pikeminnow and humpback chub habitats are rejuvenated by the very high spring flows of wetter years, production of young and recruitment are expected to be higher in moderate- and lower-flow years. The frequency of floodplain inundation could be increased (and thus greater levels of inundation achieved in average years) by removing or altering existing levees in Reaches 2 and 3. Temperature conditions for endangered fishes could be improved by releasing relatively warm water from Flaming Gorge Reservoir (up to 150C) and through flow management. Water temperatures of 18-20oC should be targeted for 2 to 5 weeks in summer and autumn in Lodore Canyon of lower Reach 1. Warmer water would increase the potential for Colorado pikeminnow and humpback chubs to reproduce in this portion of the river and would improve conditions for endangered fishes in upper Reach 2. The possibility of cold shock to Colorado pikeminnow larvae as they drift from the warmer Yampa River and into the colder Green River should be minimized by targeting Green River temperatures that are no more than 50C colder than the Yampa River during the period of drift. Additional research and monitoring is necessary to resolve uncertainties and refine the flow and temperature recommendations. Although it is beyond the scope of this report to provide a comprehensive list of research and monitoring topics, additional data collection should focus on evaluating and modifying the flow and temperature recommendations by using an adaptive- management approach. Specific experiments based on hypothesis testing should be conducted to refine recommendations on base-flow variability. Long-term monitoring should be implemented that focuses on reachwide population responses of the endangered fishes and other native and nonnative fishes to the flow and temperature recommendations. The greatest benefit will be accrued if flow and temperature recommendations are based on the observed biological response of target populations and other relevant ecological factors. xxvii