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amount of downstream movement. Nevertheless, the evidence thus far suggests that most young Colorado pikeminnow moved less than 6 miles during the winter period. We hypothesize that age-0 Colorado pikeminnow exhibit an adaptive behavior wherein in the summer and early fall they occupy backwater nursery habitats that provide refuge from the current, preferred thermal conditions, and a productive environment where prey are likely to be encountered (Tyus and Haines 1991). At this time, fish are widely distributed in the nursery area in deep and shallow backwaters. But as temperatures cool in the fall, the shallower backwaters become cooler than the main channel, even during the warmest part of the day. Fish tend to move downstream and congregate in the deepest and largest backwaters where temperatures at the mouth of the backwaters do not fall below the main channel temperature. It is in these large, deep backwaters that fish apparently overwinter (Haines and Tyus 1990; Tyus and Haines 1991; Day et al. 1999). Occasionally during the winter, the river stage increases, usually the result of an ice jam, and turns a backwater into a flow-through area. Some fish respond by moving out of the area in search of nearby low velocity habitats, but others respond by finding low-velocity micro-habitats within the area of the original backwater, perhaps behind uneven bottom contours. After ice-out and spring runoff begins, more backwaters become flow-through areas, resulting in fish movement downstream. Effects ofFluctuation Discharge from Flaming Gorge Dam We were unable to test whether fluctuating flows from Flaming Gorge Dam influenced overwinter survival, primarily because there were too few age-0 Colorado pikeminnow in our study reach to make overwinter survival estimates, and secondarily because we could not obtain the winter flow fluctuations because of the national energy emergency during the winters of 2000-2001 and 2001-20002 . Hence, we worked with the fluctuations provided during the normal Flaming Gorge hydropower generation. Winter flows over three years ranged from 991 to 3,000 cubic feet per second (cfs), but the xii