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276 cfs. A flow of 300 cfs provided at least a maximum 1-foot water depth at these three critical transects when sub-adult and adult Colorado squawfish occupied the reach up- and downstream of the three shallow water areas in late- July and early-August. A minimum "threshold flow" could not be determined using catch rate and flows because a strong positive relationship between the two variables did not exist. Although flows were known on dates of capture, this method did not provide the resolution or accuracy to identify the minimum flow at which endangered and native fishes would leave the reach. For this study, water depth measured during known low flows was the best approach for determining a minimum passage flow. The Oregon State Game Commission (Thompson 1972) suggested that the total width of stream having the specified passage depth should be at least 25% of the top width or that the longest continuous portion be at least 10% of the top width. These recommendations may be somewhat arbitrary but have been widely used and accepted by many fisheries agencies. If these guidelines are applied to the 2.3-mile reach and predicted water depths from the HEC - 2 model are used, a 1-foot water depth would be maintained across 10% of channel width at 500 cfs at transect 9 (Appendix; Table G.2.). Similarly, 300-400 cfs would be required at transect 19. Until additional water depth data can be collected at transect 20 to clarify the discrepancy between the empirical and modeled water depths, it is difficult to estimate with certainty the flow necessary for passage using the Oregon guidelines. This study also recommended a minimum passage depth of 0.8 feet for Chinook salmon and 0.6 feet each for Coho, chum, steelhead, and large trout. Although these minimum water depths are recommended for salmonid species, they do provide some starting guidelines for what minimum water depths might be required to pass large, cyprinid fishes such as adult Colorado squawfish. Based on the hydrological and biological data collected to date, a 300 cfs minimum flow is recommended. Furthermore, an instantaneous flow should be maintained rather than a mean daily flow of 300 cfs to eliminate possible daily fluctuations when flows may fall below the recommended minimum. During low-flow periods, a uniform, constant flow of 300 cfs should be reasonable to implement and should be more practical than attempting to implement flows during high-flow periods when flows are rapidly changing. A 300 cfs minimum flow, if required for the entire 123-day period of July through October, accounts for 73,191 AF of the 148,000 AF total set aside for endangered fish in the Aspinall Unit. Ideally, minimum flows should be established using habitat preference during summer low flows. This requires obtaining habitat availability and habitat use from Colorado squawfish occupying the reach. As part of the fish passageway evaluation, Colorado squawfish will be radiotagged. Habitat types selected by these fish when occupying the 2.3-mile reach should further verify the water depth and minimum flow necessary for passage. As initial minimum flows are implemented, monitoring and evaluating the response of endangered and other native fishes to these flows is essential to the recovery process. Fine tuning passage flows will be determined from the response of native and endangered fish to various low flows and from other empirical biological data collected during the first few years of operating the fish passageway at Redlands Diversion Dam. j Flow recommendations will no doubt continue to be refined as preliminary 34