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accumulate more fine substrate and ma also more readil ca tore driftin larvae and food i y y p g terns. They generally do not have the extreme temperature fluctuation seen in smaller backwaters. In both the Ouray and Mineral Bottom reaches, total habitat availability in the summer and fall, as measured in area and volume, was negatively impacted by high spring flows. There was also a slight negative relationship of habitat availability with flows at the time of sampling. Backwater numbers were not correlated with flows. However, the importance of high flows to reestablish habitat should not be overlooked. Habitat availability and quality are likely tied to a series of flow events over time (Rakowski 1997). No relationship could be detected between Colorado pikeminnow catch (CPLTE) and spring peak flows. Timing and success of spawn for all endemic Green River fish have been tied to the natural spring hydrograph and associated water temperatures (Tyus 1986). Beyond this, McAda and Keading (1989), Haines and Tyus (1990), Tyus and Karp (1991) and Tyus and Haines (1991) all pointed to a negative relationship between summer flows and Colorado pikeminnow reproduction. The inability to detect a relationship to peak flows maybe related to the high variability in this river system. Another complicating factor may be that a gap in the analysis existed in the low to moderate range of peak flows between 350 and 525 m3/s (12360- 18540 cfs), or extremely high flows above 850 m3/s (30000 cfs). The inability to develop an easily applicable model for discriminating between suitable and unsuitable backwaters is problematic, but not entirely unexpected. Extreme variability in backwater formation and availability, river conditions, and Colorado pikeminnow cohort strength between years precluded developing this simple model. However, the models produced are promising for eliminating backwaters from consideration. Effects of nonnative fishes on endangered fish is a serious concern. However, this study found a high degree of variability in the correlation of CPIJE for the various fish species. Both native and nonnative fish had examples where positive and negative correlation (p<0.10) existed between species. In this river reach, there did not appear to be a flow scenario that would benefit only native species or suppress only nonnatives. In the three highest water years of this study, nonnative cyprinid densities were higher than in the three lower water years. This maybe due to the large area of floodplain that is inundated at high flow in this reach (Rakowski 1997), creating low velocity habitat which may benefit lentic fish species. Biology: Mineral Bottom High peak flows were negatively correlated with total habitat area available in the summer and fall. Total habitat area was inimized at sampling flows above 140 m3/s (5000 cfs), and higher but variable between sampling flows of 56 to 113 m3/s (2000 to 4000 cfs). In both the Ouray and Mineral Bottom reaches the definition of quality habitat was refined to show Colorado , pikeminnow selected for habitats that are large, deep and permanent. These habitats are generally secondary (scour) channel (SC) habitats occurring below large sandbar complexes. On the Ouray study bar, the amount of this type of habitat was higher in the high water year of 1993 than in the lower water year of 1994. However, in the Mineral Bottom reach, the availability of this type of habitat was shown to be negatively associated with high spring peak flows and with sampling flows above 140 m3/s (5000 cfs). Although the strong selection of SC habitats by Colorado pikeminnow would seem to suggest that pikeminnow might increase as this habitat availability increased, this was not the case. Nonnative cyprinids also selected for SC type xi