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The objectives of this study of the San Juan River were to: 1) Document the occurrence and distribution of rare Colorado River fishes in the San Juan River; ~ 2) Characterize the fish community of the river; 3) Describe the fish habitat characteristics of the river, and assess the suitability of the habitat for supporting rare Colorado River fishes; and ~ 4) Recommend future recovery or management activities for rare Colorado River fishes in the San Juan River. Study Area The San Juan River is a major tributary of the Colorado River in the Upper Colorado River Basin Figure 1). The San Juan River drainage basin encompasses 99,200 km (Carlson and Carlson 1982). The river arises in the San Juan Mountains of southwestern Colorado. It flows southwesterly into New Mexico, turns northwest and enters Utah ~ after cutting across the extreme southwest corner of Colorado. From the Utah-Colorado state line, the river flows northwesterly for about _ 28 mi to Montezuma Creek, Utah, then flows mostly westerly to empty into Lake Powell. Encompassed in this study was the 136 mi of river from the U.S. Highway 160 bridge in Montezuma County, Colorado to _ Piute Farms Marina on Lake Powell (Figures 2 and 3). From the State ~ line to Chinle Creek (approximately 53 mi) the channel is relatively broad and braided. Below Chinle Creek the river has cut canyons into the Monument Upwarp and formed entrenched meanders. The flows of the San Juan River were historically highly variable prior to completion of Navajo Dam, New Mexico in 1963. This dam, part ~ of the Colorado River Storage Project, regulates flows for irrigation and municipal purposes (Carlson and Carlson 1982). The average discharge of the San Juan River between 1914 and 1986 was 2,577 cubic feet per second (cfs; U.S. Geologic Survey (U.S.G.S) Bluff, Utah gaging station, number 09374500). The extreme high flow recorded for the period of record 1914-17, 1927-86 was 70,000 cfs on September 10, ~ 1927. Zero flows were recorded on July 3-13, 1934 and August 24-29, 1939. Navajo Dam has moderated the natura] extremes of the yearly hydrograph. Cold water releases have decreased fluctuations in, and lowered the annual temperature regime of the San Juan River, especially above the confluence with the Animas River. Effects of the operation of Navajo Dam on San Juan River flows are greatly diminished ~ below the Animas River (VTN 1978). - 2 -