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refine the existing recommendations for spring, focusing primarily on geomorphic issues discussed in the earlier report but for which data were lacking. New studies included monitoring stream bed cross sections through years of low and high flow regimes to provide insights into minimum peak flows required to (1) maintain backwater depth through flushing the bed of accumulated fines (silt) and (2) to cleanse within-channel substrates of accumulated fines via mobilization of coarse bed materials. Study Objectives Because these populations are now in danger of extirpation, the management objective is to provide favorable if not optimum conditions that promote species recovery. Maintaining the status quo, which includes conditions that have led to population decline, will not be sufficient (Tyus 1992). This is true for managing nonnative fish, contaminants, and other impacts in addition to altered flow regimes. Therefore 'minimum' flows recommended in this report are something more than that which will enable survival of individual fish: we define minimum flows for endangered fish as those necessary for species recovery, i.e., those that promote increases in population size. The primary objectives of this study were to: 1) determine how changes in flow result in changes in riverine habitats, 2) determine habitat preferences of the endangered fish, 3) determine at what discharge the quantity and quality of preferred habitats are maximized, 4) present revised flow recommendations based on integration of new and existing data. Due to the interrelatedness of the topics addressed in this report, layout of an organizational format that clearly addresses each of the above objectives in a sequential manner was problematic. To identify which sections in the report address each of the objectives, we have listed after each heading, where appropriate, the Objective No. from the list above. Adjacent Reaches and Companion Studies We conducted this study in both the 15-mile reach and the reach (18-mile) immediately down- stream. Here we report only on the results from the 15-mile reach. Results for the 18-mile reach will later be presented under separate cover. For water management purposes, it makes sense to treat these two reaches separately because the flow regimes of each are different. However, from a biological standpoint, it is difficult to study the 15-mile reach in isolation. Many adult fish move in and out of the reach on a seasonal basis, using the adjacent 18-mile reach and other downstream reaches of the Colorado River as well as the lower 2.2 miles of the Gunnison River below the Redlands Diversion Dam. In addition, larvae of spawning adults may drift for long distances downstream of the Grand Valley and it may be many years before these young mature and return to the 15-mile reach. For the reader unfamiliar with these and other important traits of the Colorado squawfish, a brief description of its life history is provided in Appendix I. As in earlier reports, the 15-mile reach is here regarded primarily as important habitat for adult Colorado squawfish throughout the year and for razorback sucker during spring. Spawning in the 4