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availability of backwater habitat was negatively correlated with late summer- fall flows (r=-0.91, P<0.05) (Figure 11). More specifically, area of backwater habitat was maximized at 1687 cfs (average of Jensen, Ouray, and Sand Wash study areas) and number of bac'.cwater habitats was maximized at 1381 cfs (average of Jensen, Ouray, and Sand Wash study areas). Tyus et al. (1987) found that abundance and growth of YOY Colorado squawfish was negatively correlated with Iate summer-fall flows (r=-0.73, P<0.06; r=-0.88, P<0.01, respectively). During late summer/fall, catch and growth were highest in 1979 and 1980 (discharge in August-September ranged from 1600-1900 cfs at Jensen, Utah), and lowest in 1983 and 1984 (discharge in August-September ranged from 3000-4200 cfs) (Tyus et al. 1987). In the latter years, abnormally high discharge from claming Gorge Dam in late summer-fall inundated backwater nursery areas and survivorship of YOY Colorado squawfish was low. These relationships suggest that flows optimizing growth and survival of small Colorado squawfish vary with time of year, and that both reproduction and survivorship are maximized in years whose hydrographs approximate historic flow conditions. In contrast, many workers (e.g., Haynes and Muth 1984, Minckley and Meffe 1987, Nesler 1988) have suggested that abundance of non-native fishes is adversely affected when flow regimens approximate historic conditions. In years of high spring flows, Haynes and Muth (1984) found high numbers of larval Colorado squawfish and low numbers of non-native fishes in drift collections. Using seine catch-effort data from the upper Yampa River for 1980-1984, Nesler (1988) Found that total numbers of non-native fishes (red shiner, redside shiner, sand shiner, fathead minnow) were negatively correlated with spring discharge (2<0.05). However, correlation of native 40