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into account additional water released during spills. 111e is cfs now was derived through application of a simplistic habitat model as a minimum !low recommendation from the CDOW and the USF&WS. In order to meet oilIer project commitments. Reclamation determined that this minimum now could nOt be accommodated in all years: therefore. based on reduced water supply, either a 50 or 20 cfs flow would be provided downstream. In 1986. the CDOW conducted an Instream flow Assessment of the Dolores River utilizing a physical habitat simulation model called the (nstream Flow Incrcmental Methodology (IFIM) developed by the USF&WS. This model predicted an optimum flow for trout within the tailwater area of approximately 150 cfs. 11,is flow equates 10 an annual volume release of 108.597 Af. In 1990, Reclamation applied a similar If 1M model which predicted a similar optimum flow for trout. The CDOW initiated annual population monitoring studies of the tishery in 1986. Information gained from these studies over several years provides a means by which to evaluate changes in the population structure and density as well as providing an indicator of the relative quality and quantity of aquatic habitat. Since the closure of the darn in 1984 and continuing through March of 1990, project water supply was not a faetor limiting tish habitat and, aecordingly, flows provided downstream of McPhee Dam were never reduced below 78 cfs. Over this time frame, although restricted by the availability of physical habitat, the quality of the habitat was not limiting through the quality trout section of the river. Overall, the trout fishery probably reached the 78 cfs carrying capacity of the river in 1988 and 1989 when a combined estimated biomass of over 50 kglha (44.5 lb/ac) of trout occurred throughout the quality trout section. In March 1990, a dry year was designated by Reclamation and flow was reduced to 20 cfs. This flow was maintained through June 14, 1990. At this tiine, an additional 6,000 AF of water was obtained by Reclamation and flows were increased to 50 cfs for the remainder of the summer. Subsequent sampling within the tailwater area in the fall of 1990 and twice in 1991 resulted in the conclusion that the lowered flows during 1990 directly caused a significant loss to the trout fishery. Trout biomass estimates made in the fall of 1991 show a reduction in biomass to about 12 kglha throughout the quality trout section. This loss was attributed to a combination of elevated water temperatures' in the Dolores River in the lower half of the quality trout section and a severe reduction in available physical habit~t at reduced flows. Further, it was concluded that during summer periods a 50 cfs flow would not provide suitable water temperatures for trout throughout the entire 12 mile section of the trout fishery. In addition.to causing elevated water temperatures, a 50 cfs flow would also not allow sufficient depth within several riffle areas of the stream to allow larger trout to migrate upstream to escape warmer sections of the river. It was estimated that, at a minimum, a 70 cfs flow would be required to allow for the upstream movement of trout. In November 1990, an interim operating agreement was agreed to between Reclamation and the Dolores Water Conservancy District allowing for the temporary (three years) change in operating McPhee Reservoir. This agreement provided a pool ofwarer of no less than 30,100 AF of water that could be released downstream for fishery purposes. Also, during a designated spill, managed or real, there would be no accountable reduction in the remaining volume of water left within the fishery allocation. Commensurate with the approval of this agreement, aquatic studies were undertaken to bener identify minimal seasonal flow needs required to maintain adequate water quality necessary to avoid significant losses to the trout fishery. Spills occurred during all three years allowing for additional water to be released downstream during the remainder of the water year. 'It was decided that the majority of this additional water be spent during summer periods to fully offset the effects of elevated ambient air temperature and to provide better angling conditions for tishennan. Therefore, Ihe adequaq of a 30,100 Af tish pool has never been directly tested. The trout fishery had recovered significantly by the fall of 1992. . Based on biomass estimates made in 1992 and in 1993, the fishery supported an estimated 44 and 70 kF/ha of trout, 'respectively. However, the biomass estimate made in 1993 includes tish that were lost from the reservoir the previous spring during a spill release. Accordingly, agency biologists agree it represents a much higher figure thm whatlhe long.tenn carrying capacity of Ihe river was at existing base flow conditions. Overall, the data clearly indicates that pool management is a much more efficient way to maimain the tail water trout fishery in the Dolores River. In a 23