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. . Protecting what remains of the best habitat conditions for the rare fishes in the Yampa River basin during the Spring may be achieved by not further altering the magnitude, frequency, duration, or timing of sprin9 flows as described under current environmental baseline conditions (Table 2). Major deviations from the current environmental baseline flows will likely eliminate any hope for recovery and maintenance of the rare fishes in the Yampa and Green River basins. The Yampa-Green ecosystem constitutes the best remaining riverine habitat for Colorado squawfish and razorback sucker. Caution was exercised in providing flow recommendations for these fishes for fear they will be driven to further decline. 2. Summer (June 22 - September 22) Colorado sauawfish Spawning and egg deposition of Colorado squawfish occur in association with the declining flows, decreasing sediment transport, and increasing temperatures of summer. A gradual decline in summer flows following spring scouring of spawning substrate would maintain a natural sediment transport equilibria, and prevent siltation of spawning substrate. The growth, development, emergence, and downstream drift of larvae are also related to this regimen. Downstream nursery areas are created by high spring flows, but maintained as productive fish habitats by the declining flows. Razorback sucker Late spring and early summer is presumably the time when recruitment fails in this species. This failure has been linked elsewhere with predation by introduced species, and may be associated with loss of flooded bottomlands and lower river temperature. Lower flows tend to favor establishment and proliferation of potential competitor species by creating shallow habitats and warmer temperature regimens. Humoback chub Rapidly declining summer flows could adversely affect spawning and nursery habitat of the humpback chub in Yampa Canyon by concentrating fishes in suboptimal habitats and increasing the potential for disease, competition, predation, and hybridization. Low flows probably aid the growth of channel catfish, a presumed competitor. Gradual decline of flow from peak spring condition is favored for this species. Summer recommendations Gradual decline from spring peak flows are needed to maintain favorable habitat conditions. Present flows should be maintained for the period. June 22-August I, followed by flows near the 50% exceedence value. These flows would be compatible with larval transport for the remaining summer period (AU9ust I-September 22) and maintenance of nursery habitats for Colorado squawfish in the Green River in August and September (flows of about 1800 cfs at Ouray, Utah). 5