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Final Report 4-7 September 2000 regulations, mechanical removal, chemical eradication, and management of flows to benefit native fishes and suppress the abundance of nonnative fishes. The last option is important in the context of this report because occasional high or very high spring flows, and summer conditions resulting from higher spring flows, have been correlated with reduced abundance of channel catfish (Chart and Lentsch 1999) and nonnative cyprinids in shoreline habitats of the Colorado, Yampa, Green, and San Juan Rivers (McAda and Kaeding 1989; Haines and Tyus 1990; Muth and Nesler 1993; Gido et al. 1997; McAda and Rye11999; Trammell and Chart 1999). Effects of high spring flows on many of the common native fish species have been neutral to positi ve (e.g., Muth and Nesler 1993; McAda and RyeI1999), but short-term decreases of some native fishes, including Colorado pikeminnow, have been documented (Haines and Tyus 1990; Tyus and Haines 1991; McAda and RyeI1999). Exact mechanisms for lowered abundance of nonnative fishes associated with higher spring flows are unknown but may include (1) flushing fish downstream; (2) reducing their ability to successfully reproduce (high flows that persist later into the summer are often cold and may also reduce the abundance of warm-water nonnative fishes by inhibiting early spawning or reducing hatching success [Muth and Nesler 1993]); (3) reducing backwater habitat where many of these species complete their entire life cycle; or (4) a combination of the three mechanisms. Concerns exist within the Recovery Program about overbank flooding associated with high spring flows and the potential beneficial effects of floodplain inundation on the abundance of nonnative fishes in rivers. Preliminary conclusions by Crowl et al. (1998b) indicate that although the density of nonnative fishes in the middle Green River exhibited localized increases associated with floodplain inundation and draining, those increases were temporary. They also reported that preliminary evidence suggests patterns of weak, inconsistent interactions between native and nonnative fishes in floodplain sites.