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29 summer. Although fast runs and riffles were used during the summer. they were not used during the winter. The colder water temperatures in winter which cause lower metabolic rates may account for the avoidance of high velocity sites. Absolute area of pools increases as flows decrease and slow runs lose velocity. Because Qsmundson et al. (1995) did not sample fish during low flows in the winter (because there were no low flows), they could not determine if pools would still be preferred in the winter at lower flows. Therefore. they recommended winter flows at the moderate flow level which maximized weighted area of preferred habitats, Spring (April-July): Qsmundson and Kaeding (1989) reported that squawfish use' of low velocity habitats such as backwaters and flooded gravel pits is - greatest during the spri~g runoff. It is believed that squawfish use these habitats during the runoff to escape the high velocity, low temperature flows of the main channel. Because backwaters. flooded gravel pits. and other low velocity habitats are considerably warmer than the main channel during the runoff. these habitats allow squawfish to extend their growing season substantially. The earlier warming of these habitats may also be important in enabling squawfish to reach spawning condition by the time flow and temperature in the main channel are optimum for spawning. Qsmundson et al. (1995) reported that the numbers of backwaters and flooded gravel pits increases with increasing spring flows (although the number of backwaters eventually decreases as increasing flows convert backwaters to sidechannels. the number of other low velocity habitats likely increases as increasing flows inundate additional bottomlands). The decrease in the magnitude, duration. and frequency of high spring flows. then. decreases the quantity and the duration and frequency of availability of important low velocity. higher temperature habitat in the spring. This could be affecting squawfish growth and spawning success, Also. the quantity and frequency of availability of inundated floodplain depressions used by razorback suckers for spawning is dependent on the magnitude and frequency of spring flows necessary to inundate these areas, The decrease in the magnitude and frequency of spring flows necessary to inundate floodplain depressions is believed to be largely responsible for poor razorback sucker spawning success. Biolooical Environment Food supply, predation. and competition are important elements of the biological environment. Food supply is a function of nutrient supply and productivity, which could be limited by the presence of contaminants. The modification of flow regimes, water temperatures, sediment levels. and other