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generation fluctuations at Flaming Gorge Dam were minimized. In Lodore Canyon, drought in 2002 to 2006 resulted in low base flows (2005 base flows were moderate level), and thermal regimes in the study area were more similar to those in the pre-dam era than during any other post-impoundment period. This ensured a close match of Green and Yampa River water temperatures during drought years when Colorado pikeminnow larvae were drifting downstream from the Yampa River in summer. Green River peak flows in Whirlpool Canyon in the pre-impoundment period showed a typical dome-shaped hydrograph, with low late-summer, autumn, winter, and early-spring base flows, rising to a peak in late spring and early summer. Post-impoundment Green River peak flows in Whirlpool Canyon were lower and arrived earlier than historically, an effect of Flaming Gorge Dam. Whirlpool Canyon flow peaks during 2002 and 2004 were lower than the historical average while the 2003, 2005, and 2006 peak flow exceeded the average historical condition (1946 to 1962). Base flows in Whirlpool Canyon in the 2002 to 2006 period matched the historical average pattern reasonably closely. Thermal regimes in 2002 to 2006 were similar to historical ones because dam-related cooling was probably overwhelmed by enhanced warming during low flows, although 2005 water temperatures were cooler. We used raft-based electrofishing gear, seines, drift nets, and trammel nets to sample Green River fishes from Browns Park downstream to Island-Rainbow Park. A total of 209,466 specimens representing 9 native and 19non-native species and 7 hybrid combinations were captured by all sampling gears during 2002 to 2004. When data obtained with all gears were combined, native fishes in the 2002 to 2004 period comprised only 10.3% of total catch and non- natives were 89.3%; the remaining 0.4% were hybrids. In the 2005 to 2006 period, an additional 68,466 specimens representing 11 native and 21 non-native species and 6 hybrid combinations v