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parameters used (depth, velocity, and substrate) were not accepted as the only factors required by the fish, and conflicting flows have been obtained for different species and life stages in the same location (Tyus 1992). Recent studies by the Service have focused on developing flow recommendations based on current biological theory; statistical analysis of the relationship between streamflows, habitat, and fish populations; and the use of professional judgment to integrate information into a flow recommenda- tion that makes biological sense. Results have indicated that the endangered fish require flows that more closely mimic the natural flows that existed historically in the basin. These flows, which are characterized by high flow in the spring and low stable flow for the summer, fall, and winter periods, are closely associated with (See Figure 2 Page 53) some of the important life history events of the Colorado squawfish, humpback chub, and razorback sucker. The Service's flow recommendations for the endangered fish have not been readily accepted by state agencies as technically adequate for appropriating, acquiring, and/or legally protecting the instream-flow needs of the fish. One concern is that the flow recommendations have been based on empirical data and professional judgment rather than analytical habitat models. In addition, the Colorado Water Conservation Board (Conservation Board), which is responsible for review, approval, and subsequent appro- priation of instream-flow water rights in Colorado, believes the Service's recommendations and approach will not allow for a determination of the "minimum" flow needed to recover the species, or what the impact would be on the fish if flows less than the recommended amounts were appropriated. In addition, Reclamation and the Western Area Power Administration have expressed concern that the Service's flow recommendations for the Green River, especially for the spring and winter periods, are not biologically defensible and need further refinement. Several actions have been taken through the recovery program to resolve the disagreement over the Service flow recommendations and methodologies. First, Dr. Jack Stanford, a noted aquatic ecologist from the University of Montana, has been retained to: (a) complete a comprehen- sive review of past and ongoing instream-flow activities, methods and knowledge related to the quantification of the instream flows needed for recovery of the four endangered fish species in the upper Colorado River and Green River subbasins; (b) identify technical and non-technical issues related to the instream-flow activities and the Service's instream-flow recommendations; and (c) develop an action plan and provide recommendations to resolve the technical issues related to quantifying the instream-flow needs of the endangered fish. Dr. Stanford's review, which will be complete in July 1993, will be overseen by the Instream- Flow Subcommittee of the Recovery Program. Second, an additional five years of research will be conducted to refine and validate the winter and spring-flow recommendations for the Green River contained in the Service's biological opinion on the operation of Flaming Gorge Dam. Reoperation of Federal Reservoirs The reoperation of federal reservoirs to provide instream flows for the endangered fish is an important element of the recovery program. The focus has been on three Reclama- tion reservoirs: Flaming Gorge on the Green River, Blue Mesa (or the Aspinall Units) on the Gunnison River, and Ruedi on the Frying Pan River. (See Figure 2 Page 53) Ruedi Reservoir on the Frying Pan River, Colorado, is providing flows in the late summer and early fall to enhance flows for endangered fish in the Colorado River approximately 150 miles downstream. Releases are being targeted at a 15-mile reach of the Colorado River immedi- ately upstream of the Gunnison River that is severely impacted by irrigation diversions. The reach is a concentra- tion area for adult Colorado squawfish and, in the 1970s and early 1980s, was used regularly by razorback suckers. In 1989, Reclamation, the Service, and the Conservation Board entered into a 40-year agreement to provide 10,000 acre feet of water from Ruedi Reservoir to enhance flows in the 15-mile reach during the late summer and early fall. In 1991, the Service requested an additional 10,000 acre feet of water from Ruedi Reservoir (totaling 20,000 acre feet) because a surplus supply of water was available in Ruedi, and other efforts to acquire water for the 15-mile reach through the Recovery Program had not materialized. An agreement was executed between the Service, Reclamation, and Conservation Board in 1991 and again in 1992 to provide the additional 10,000 acre feet. Under the agree- ments, Reclamation releases water from Ruedi according to the schedule provided by the Service, the Conservation Board and the State Engineer to protect the releases through the 15-mile reach from diversion, and the Service evaluates the effect of the releases on the endangered fish. Flaming Gorge Dam in northeast Utah regulates flows in the Green River. Since the early 1980s, studies have been conducted to evaluate the impacts of the dam operation on the endangered fish. The results of these studies are now being used by the Service to develop its biological opinion on the operation of Flaming Gorge Dam pursuant to Section 7 of the Endangered Species Act. A draft biological opinion issued in early 1992 outlined a reasonable and prudent alternative to preclude jeopardy to the endangered fish from the continued operation of the dam. The reason- 49