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of a minimum flow for passage was developed from 1) fish observations and collections and 2) empirically recorded water depths during low-flow periods and modeled hydrologic data. With the fish passage at Redlands operational, it is imperative that a minimum flow for passing Colorado squawfish and razorback sucker be identified to allow unimpeded up- and downstream movement of the endangered fishes between the passage facility and confluence with the Colorado River. The minimum flow passage recommendation in this study was based on the following assumptions: the 1. Low-flow conditions make passage for sub-adult and adult Colorado squawfish and other native fishes in the reach impossible. Fish become displaced and move downstream to the Colorado River until flows increase and habitat conditions improve. During periods of sustained low flows, both habitat quantity and quality are reduced. Increases in water temperatures and low oxygen can create suboptimal conditions for fish. 2. Sub-adult and adult Colorado squawfish require a water depth of at least 1 foot to negotiate shallow-water locations in the reach. The body depth of a large, female Colorado squawfish can be approximately 6-10 inches. A fish with a body depth of 10 inches would physically require at least 1 foot of water to swim and negotiate shallow-water habitats. The 1-foot water depth was arbitrarily selected by professional judgment. 3. Water depth was used solely to determine if suitable habitat existed during various low flows for sub-adult and adult Colorado squawfish passage. This study collected microhabitat data (i.e., depth, velocity, and substrate) from each Colorado squawfish collected. General habitat types (i.e., backwaters, eddies, pools) from captured fish were recorded but not used. It is acknowledged that depth, velocity, and substrate are all important habitat components in determining habitat preference. However, microhabitat-use data from sampling with electrofishing or netting are less accurate and reliable than use data from radiotagged fish because the location and habitat used prior to and following capture may differ greatly. Therefore, electrofishing data were not used to determine habitat use. 4. The 2.3-mile reach is within critical habitat and has importance in addition to a passage corridor based on the high use by sub-adult and adult Colorado squawfish from March to September from past radiotelemetry contacts and from fish capture and sighting data. Although it is uncertain how far upstream larval Colorado squawfish originated, the capture of larval fish in 1986 and 1992 from this reach suggests that management should include consideration of its value as potential feeding and spawning habitat. This various does not recommend flows necessary for enhancing or maintaining life stages of endangered fishes in the 2.3-mile reach. Very little ation is available for razorback sucker use in the 2.3-mile reach. For 11