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METHODS The number and area of backwaters were examined during seven flows at the Island Park, Jensen, Ouray, and Sand Wash sites during 1987: 142 on May 30, 1987; 71 on July 7, 1987; 55 on July 19, 1987; 53 on July 22, 1987; 46 on August 17, 1987; 45 on August 1, 1987; and 37 m3/s August 9, 1987. These flows were selected to establish upper and lower limits around what are considered potential summer releases from Flaming Gorge Dam. Three flows were examined at the Mineral Bottom site: 108 on August 1, 1987; 98 on July 7, 1987; and 79 m3/s on July 1, 1987. Flows were controlled by varying releases from Flaming Gorge Dam. The USGS (U.S. Geological Survey) Jensen gauge - approximately 30 Ian below Island Park, 10 Ian above Jensen, 64 Ian above Ouray, and 124 Ian above Sand Wash - was used to estimate flows at the four upper sites. This was the closest gauge available to each site in the study and it may reflect flow at some sites more accurately than others. Flows at Mineral Bottom were estimated by the USGS Green River, Utah, gauge located about 112 Ian above the site. Flows were gradually stepped down during late spring and summer to mimic the descending limb of a "natural" Green River hydrograph. When flows were stabilized at each site, color infrared aerial photography was acquired at an approximate scale of 1:4,000. However, because of weather conditions the 46 m3/s flow was not photographed in proper sequence and was actually the last flow attained. This incident may have effected backwater availability because they did not form during a gradually descending hydrograph. Field trips were taken to familiarize the photointerpreter with backwater delineation and to place panel markers at specified distances at each site to verify and correct photographic scale. The photo interpreter was on the river at each site (except Mineral Bottom) during each flow event. Three backwaters were examined in the field at each site, during each flow (except Mineral Bottom) and were later identified on aerial photographs using USGS quadrangles. Ground-truth information assisted the photointerpreter in recognizing backwaters as they appeared on aerial photographs. The river channel, backwaters, and sandbars were delineated on mylar overlays fitted on the aerial photographs. Backwaters were separated according to area: .s,20, > 20.s,200, > 200.s,500, >500.s,1,000, and> 1,000 m2. To maintain interpretation accuracy, map bases of the same scale as the photography were created using roads and other prominent features delineated on photographs. These were compared to USGS 1 :24,000 quadrangles to provide geographic reference. Following transfer of photointerpreted data to map overlays, the information was digitized into a GIS utilizing Geographic Entry System software. Digitization was done in vector format using a digitizing tablet linked to a display screen. Software and peripherals were run by a minicomputer. Regression analyses (Bailey, 1981) were conducted for flow versus backwater area and flow versus backwater number at the four upper sites. Linear regression was not conducted on Mineral Bottom data because only three flows were mapped and flows at this site are difficult to control because of its distance from Flaming Gorge Dam. Linear regression of flow versus area was analyzed for flows from 37 to 71 m3/s for the Island Park, Jensen, and Ouray sites. Regressions were run with and without the 142 m3/s flow, acquired during the spring, because it was outside the range of normal operations for the summer season when yoy Colorado squawfish are entering backwaters. The 46 m3/s flow was also deleted at the Sand Wash site because this flow had not reached the site when the photography was acquired. 2