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I I I I I I I I I I I I I I I I I I I operations at the Uravan site. Based on the magnitude of changes that occurred on the site in 1990, it appears that clean up is proceeding at a regular schedule, The recent construction and closure of McPhee Dam on the upper Dolores River in 1984 has also significantly affected the Dolores River system. Capture and storage of runoff flows in McPhee Reservoir have reduced the magnitude and altered timing of spring flow peaks below the dam. This effect is somewhat attenuated below the confluence of the San Miguel River, which is free flowing and still exhibits a relatively normal hydrograph. Late summer and early fall base flows in the Dolores River have been augmented by more constant base releases from the dam during these periods. Prior to the closure of McPhee Dam in March of 1984, the Dolores River above the confluence of the San Miguel, was often dewatered during this period from irrigation diversions. Although the potential impacts of McPhee Dam operations associated with altering the timing and magnitude of peak runoff need to be addressed further, augmented late summer flows may represent a beneficial change for native fishes utilizing the Dolores River drainage. Augmentation of late summer and early fall flows from McPhee Dam may also improve water quality in certain reaches during base flow periods. This particularly applies to the 10 mile reach of the Dolores River from the confluence of the San Miguel River upstream to Paradox Valley. Saline ground water inputs in Paradox Valley would be diluted to a greater extent base flows. Benefits of this diluting effect would be less profound below the confluence of the San Miguel River, which generally doubles the flow of the Dolores River. The beneficial effect of dilution would only pertain to the period of time when releases from McPhee Dam increase flows beyond normal pre-dam levels. During the season when historic flows are less than the pre-dam condition (Le. spring runoff), salinity would be increased in the Dolores River. 2.0 STUDY AREA This investigation was conducted in the Dolores River, from Slickrock, Colorado (RM 124.7) to the confluence of the Dolores and Colorado rivers (RM 0.0) (Figure 1). The Dolores River above Slickrock to the Bradfield Bridge (RM 124.7 - RM 177) is currently being investigated by the Colorado Division of Wildlife (CDOW) as part of a river otter reintroduction program. Fisheries information collected by the CDOW in this reach will be provided to BIO/WEST early in 1991 (Beck 1989). This information will be evaluated and incorporated into the Dolores River Native Fish Habitat Suitability study at that time. This evaluation will also be used to determine if additional fisheries work will be required for the study in 1991. For purposes of this study, the 125-mile study reach was divided into five subreaches. The Slickrock to Bradfield Bridge reach will become the sixth subreach in the study area as the CDOW information is incorporated into the results. Designation of subreaches was based on those used by Valdez et aL 1982. The study reach for this project extends approximately 48 miles further upstream than the reach surveyed by USFWS, consequently one additional subreach has been added to encompass this section. The five subreaches used in this study are defined as follows: Subreach I: Dolores-Colorado River Confluence (RM 0.0) to Utah-Colorado Stateline (RM 22.7) (Corresponds to USFWS Stratum T) Subreach II: Utah-Colorado Stateline (RM 22.7) to Salt Creek (RM 41.3) (Corresponds to USFWS Stratum U) 3