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base flows that more closely approximated historical levels. Increased releases later in summer to meet federally mandated discharge levels in the Green River at Jensen, Utah, caused water temperature in the downstream portion of the regulated reach to peak early in summer, but then decline the rest of the summer rather than continue to warm. Re-creation of physical habitat similar to what historically occurred in Lodore Canyon will require discharge regimes that more closely approximate historical conditions and additional warming of water in summer. Composition and reproductive status of the fish community in the regulated reach, 1962- 1 ii 1996.-The historical fish community of the Green River upstream of the Yampa River has undergone dramatic shifts in fish species composition and abundance at least two times since 1962 in response to dam construction and river regulation. The largest impact was from creation and operation of Flaming Gorge Reservoir (Vanicek et al. 1970). After normal operations began in 1967, all native fishes were very rare, and reproduction was essentially absent throughout the entire regulated reach (Vanicek et al. 1970, Holden and Crist 1981). Cold water fishes replaced native taxa, including the four big-river forms bonytail, humpback chub, Colorado pikeminnow, and razorback sucker, all of which are now federally listed as endangered. Apre-impoundment fish removal program also likely reduced distribution and abundance of native fishes in the regulated reach; subsequent re-invasion likely did not occur because of cold releases (Holden 1991). Following enhancement of summer water temperatures in 1978, a total of nine native fishes was detected in the regulated reach. Reproduction by several, including flannelmouth and bluehead suckers and speckled dace was documented (Holden and Crist 1981). Adults of rare native fish, including Colorado pikeminnow and razorback sucker, were captured in low numbers but reproduction was not detected. Immediate invasion of the regulated reach by several obligate warm water non-native taxa, and subsequent reproduction, also demonstrated the powerful role that water temperature played in regulating fish distribution and community composition. Discharge modifications implemented in 1992, and associated thermal enhancement; also appeared to further shift the fish community and habitat in the Lodore Canyon reach of the Green 27