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In 1993, this 2.3-mile reach was identified as a priority area for instream flow protection. The Gunnison River from the confluence of the Colorado River upstream to the confluence of the Uncompahgre River (56 river miles) was designated critical habitat for both the Colorado squawfish and razorback sucker in 1994 (59 FR 13374-13400) under authority of the ESA. The Redlands Diversion Dam, located 2.3 miles upstream of the confluence with the Colorado River, has prevented the upstream movement of all fishes and further reduced Colorado squawfish numbers in the Gunnison River by preventing movement upstream of the dam since it was constructed in 1918 (Wiltzius 1978; Valdez et al. 1982b). The Redlands Diversion Dam, privately owned and operated by the Redlands Water and Power Company, is a 12-foot high barrier that, prior to 1994, diverted 750 cfs of water from the Gunnison River into a canal on the left abutment for 50 weeks each year. In 1994, an additional 100 cfs was decreed to Redlands for hydroelectric generation. Except for occasional, prolonged low- flow periods in the Gunnison River drainage and one week each in the spring and fall in which the canal is drained for inspection and maintenance, an average of 750 to 800 cfs is diverted into the power canal year-round. This flow is conveyed down-canal for irrigation water (about 80 cfs) and hydroelectric generation (about 770 cfs). Thus, Redlands now can operate the diversion dam to divert a maximum of 850 cfs into the canal. During the winter, Redlands diverts about 750 cfs for hydroelectric use. During low-flow periods, water flow has essentially ceased for several days in the 2.3-mile because water was withdrawn from the river by the Redlands Canal . Dewatering routinely occurred in the summer months of June through September when irrigation demands were highest. Flows are lowest during July and August since construction of-the Aspinall Unit reservoirs upstream. This resulted in loss of habitat, loss of passage for fishes attempting to move upstream or downstream to the Colorado River, and possible stranding in the plunge pool and 2.3-mile reach. Interim Cooperative Water Agreement A 5-year memorandum of agreement among the BR, FWS, and the Colorado Water Conservation Board was finalized in August 1995 to furnish water from the Aspinall Unit for the benefit of endangered fishes in the Gunnison and Colorado rivers (Contract No. 95-07-40-R1760). This interim contract is designed to provide 300 cfs during "low-flow conditions" for July through October in the 2.3- mile reach of the Lower Gunnison River downstream of the Redlands Diversion Dam. Moreover, this agreement is an important step because it provides legal protection of flows in critical habitat that will protect and enhance aquatic habitat to benefit endangered fish. Purpose and Objectives The purpose of this investigation is to establish a minimum streamflow recommendation that will allow passage of sub-adult and adult Colorado squawfish and razorback sucker by obtaining biological and hydrological data in the 2.3- mile reach of the Lower Gunnison River. 5