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in the Grand Valley begins and flows in the 15-mile reach are reduced. During late April to early May, flows from spring-runoff increase greatly and the high-flow period in the 15-mile reach begins and lasts through early July. Radiotelemetry data indicate that as flows increase in late April, there is a substantial increase in use of backwaters by Colorado squawfish (Osmundson and Kaeding 1989). In May and June, flows increase dramatically and riverside gravel pits become flooded; many squawfish then move into these protected off-channel habitats. The use of gravel pits and backwaters reaches a yearly peak at this time. Though this is the period of highest river flow, deep-water (> 4.5 ft.) sites are little used, par- ticularly during April and May. Off-channel, protected sites are of zero or low (< 1.0 ft./sec) velocities. The Physical Habitat Simulation Method- ology (PHABSIM), used to develop summer flow recommendations, cannot be used in developing flow recommendations for the spring period because gravel pits, backwaters, and eddies collectively comprised 53.5% of the habitat used by adult squawfish during this time, habitat types that are not represented in the current PHABSIM site and which PHABSIM has diffi- culty modeling. Perhaps most importantly, spring flow recommendations should not be based solely on the spring habitat needs of adult squawfish. High flows during spring provide other important benefits to the system, that is, year-round benefits perhaps of overriding importance to the overall population. Spring Flow Effects on Habitat ComplexitX High flows during spring create and maintain the braided channel morpholo- gy that provides a variety of important habitat types, such as side chan- nels, pools and backwaters. Without these high flows, the channel would become simplified with a concurrent loss of habitat heterogeneity. Pools 5