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Historically, flows in the San Juan River were highly variable before 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 highest flow recorded for the period of record (1914-17 and 1927-86) was 70,00 cfs on 10 September 1927. Zero flows were recorded on 3-13 July 1934 and 24-29 August 1939. Navajo Dam has moderated the natural extremes of the yearly hydrograph. Co 1 d water releases have decreased fl uctuat ions 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). METHODS Sampling of the river was stratified by river miles which were designated on a base map (U.S.G.S. 7.5 minute quadrangle), with Piute Farms, Utah designated RMI zero and subsequent miles numbered upstream (Figures 2 and 3). All data collected were referenced to the nearest 0.1 RMI. The river was blocked into 5-mi reaches for el ectrofi shi ng and sei ni ng. The 5-mi reaches were numbered consecutively upstream and assigned reach code numbers (e.g., RMI 0-5 = reach code 1, RMI 5-10 = reach code 2, etc.). SorinQ ElectrofishinQ A 16-foot rigid-bottom aluminum boat outfitted for electrofishing was used during the spring electrofishing efforts. Power for electrofishing.was produced with a Honda EMS4500 generator (Honda Motor Co., Tokyo, Japan). Pulsed direct current was produced with a variable voltage pulsator (VVP-15, Coffelt Elec- tronics Inc., Englewood, Colorado). Standardized electrofishing runs were made from Four-Corners to Sand Island (RMI 136-87) and consisted of three electro- fishing runs through each 5-mi reach (Figure 2). First run covered the best habitat; second run covered right bank; and, third covered the left bank. All fish stunned in the first mile of each 5-mi reach were captured with dip nets, enumerated and recorded by species for that river reach. Fish that were missed and could be identified to species were enumerated and recorded. Because of their abundance and relative ease of identification, carp stunned in the first mil e segment were counted, and no attempt was made to net them. Catch' rates (fish per mile and fish per hour) were calculated from this standardized electrofishing data. Total electrofishing time (seconds), as indicated on the VVP timer, was recorded for each I-mi segment and 5-mi reach. Only rare fishes were captured in the remaining 4-mi of each 5-mi reach. Rare fish were weighed (+/- 20g) and measured (TL mm) and those longer than 200 mm TL were marked with a numbered blue Carlin tag. After the completiGn of the spring standardized electrofishing, additional target electrofishing was conducted. These efforts were directed solely at collecting rare endemic Colorado River fishes. During additional target 8