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Shallow backwaters with a large surface area in the Ouray area that were seasonally permanent after runoff subsided were generally warmer compared to upstream backwaters at Island Park and Jensen; they had higher concentrations of nutrients, particulate organic material, and greater densities and weights of benthic macroinvertebrates, and moderate chlorophyll a levels. Benthic macroinvertebrates were the principal food source for most young fish, except suckers. The river is one nutrient source for backwaters. Increased concentrations of some nutrients in the river at Ouray compared to Jensen, result from upstream agricultural runoff and return flows (abstracted from Executive Summary). Study 6: Mapping of Important Backwater Habitats of Colorado squawfish. Report 18- Comprehensive Report (1986-1988) on the Effects of Green River Flows on Backwater Habitat Availability as Determined by Remote Sensing Techniques (Pucherelli and Clark 1989). Aerial photography and videography can be used successfully to determine backwater availability in the upper Colorado river basin in response to varying flow regimes. These techniques should also be applied to future riverine habitat monitoring programs for the Green and Colorado rivers. A flow range of 28.3 to 50.94 m /s at the USGS Jensen gauge will produce more backwater area and numbers on the upper Green River. Flows above 50.94 m3/s had a detrimental effect on backwater development under our study conditions. A gradually decreasing hydrograph during summer months appears to be a required condition for maximizing backwater availability. High flows may be required before young-of-the-year Colorado squawfish enter the system to maximize backwater availability. Backwaters are much more numerous and substantially larger in the Green River above Desolation Canyon than below it. The upper nursery area (Tyus et al. 1987) had the greatest amount of backwater habitat (Conclusions). PART III. HABITAT USE AND STREAMFLOW NEEDS OF COLORADO SQUAWFISH, HUMPBACK CHUB, AND RAZORBACK SUCKER The following section summarizes habitat use and streamflow need information for Colorado squawfish, bonytail chub, humpback chub, and razorback sucker in the Green River. Habitat requirements and factors limiting the distribution and abundance of each species were obtained from data presented in the preceding section and from a review of pertinent literature. Colorado squawfish Adult Adult Colorado squawfish are widely distributed in the Yampa and Green rivers, where the fish is considered most abundant (Holden and Stalnaker 1975, Tyus et al. 1982ab, Behnke and Benson 1983, Tyus 1990}. In the mainstream Green River, adults were most prevalent in upper and lower sections (Tyus et al. 1987). During the winter months, adult Colorado squawfish used backwaters (ephemeral along-shore embayments), runs, and eddies, but were most common, and presumably feeding, in shallow shoreline areas and "slackwaters" (Valdez and Masslich 1989, Wick and Hawkins 1989). Colorado squawfish selected certain river reaches in the Green and upper Yampa rivers and generally remained active in these areas all winter (Valdez and Masslich 1989, Wick and Hawkins 15