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Reservoirs Blue Mesa Reservoir is a major fishery in Colorado with kokanee salmon, rainbow trout, and lake trout being the dominant sport fishes. Changes in reservoir operations can affect loss of fish through reservoir outlets, the thermal regime of the reservoir, and the overall reservoir productivity. May through September reservoir levels would average approximately 5 feet lower under the flow recommendations and would be over 30 feet lower in very dry years. Reservoir productivity and other factors would be negatively affected. Loss of fish through entrainment would have a negative effect on reservoir fisheries, . but the significance has not been studied. Higher releases may increase loss of fish, particularly schools of kokanee salmon. Loss of productivity and entrainment are of significant concern to the Colorado Division of Wildlife due to the value of the kokanee fishery. Downstream The river downstream of Crystal Dam has developed into a Gold Medal trout fishery, dominated by naturally reproducing rainbow and brown trout. Rainbow trout reproduction has been reduced greatly by whirling disease in recent years but the river retains a Gold Medal quality fishery. Trout populations have been monitored for over 20 years by the Colorado Division of Wildlife under a variety of flows. Significant problems occur to the fishery under several flow conditions. Dewatering of brown trout eggs can occur when flows drop after the fall spawning period, and both rainbow and brown larval fish have a poor survival rate during high, fluctuating flow periods in the spring and early summer. Peak flows, if gradually ramped and if occurring in the mid-May to June 1 range, should not significantly affect the young fish. Optimum adult fish habitat flows are probably around 800-1,000 cfs, while the 300 cfs minimum flow has been shown to support the fishery over short time periods. The Colorado Water Conservation Board holds a junior 300 cfs instream flow right and Reclamation has operated the Unit to maintain this minimum flow since the 1980's. Spring peaks in May, with appropriate ramping, as described in Model runs B, C, and D; should not be detrimental to the trout fishery and would help maintain river channel habitat conditions for both trout and aquatic insects. Long-term impacts of peak flows on habitats such as overhanging banks have not been addressed. The flow recommendations would increase the number of days flows are reduced to the minimum of 300 cfs from approximately 1,129 days to 1,365 days (or from an average of 43 days per year to 53 days per year) during the 26-year study period, thus having a slight adverse effect on the trout fishery. Table B-6 in the attachments shows average monthly flows in the trout fishery for the alternative model runs. Increased use of spillways under the model runs would result in increased maintenance of Aspinall Unit structures, and this would increase the frequency of flow interruptions or fluctuations. The limited riparian corridors in the semi-arid climate of western Colorado provide the most valuable wildlife habitat in the area. The riparian habitat provides valuable nesting and migration habitat for a number of birds. Limited waterfowl nesting occurs along the Gunnison River, but a significant winter waterfowl population uses the river. Regulated flows downstream from the Unit have affected riparian areas in two ways: reduced scouring flows have expanded areas of riparian shrubs along the river banks, and in the National Park, box elder vegetation and other riparian species; and the reduced high flows have limited cottonwood regeneration, primarily along the lower Gunnison River. 11