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endangered fishes in the Colorado River basin. The Green River directly downstream of Flaming Gorge Dam formerly provided habitat for Colorado squawfish, razorback sucker, bonytail, and humpback chub. However, following closure of Flaming Gorge Dam, those warmwater species disappeared in the Green River from the dam downstream to the Yampa River. Cold temperature regimes are presumed to be unsuitable and may be the primary factor for absence of Colorado squawfish and other rare spPCies there. Modification of temperature through release of warmer surface water from Flaming Gorge Reservoir has been suggested in the Biological Opinion on Flaming Gorge Dam as a strategy to restore the Green River upstream of the Yampa River. Increased water temperature may provide more habitat for rare fish species, if appropriate water temperature regimes can be provided in the Green River upstream of the Yampa River. Colonization of the upper Green River by one or more .endangered fishes may eventually lead to establishment of other spawning areas and enhance recovery efforts for those species. Description of Work A new start study under the lead of the LFL. Study goal-Data from this study will provide an initial step to evaluate potential for restoration of the Green River upstream of the Yampa River for rare fishes. Restoration potentially includes expansion of the ranges of several rare fishes as well as provision of additional spawning localities. Study objectives-1.) evaluate the current fish fauna of the reach #rom Flaming Gorge Dam downstream to the Yampa River, 2.) determine relationship of flow and annual temperature regimes to the current distribution and abundance of fish species in the Green River upstream of the Yampa River, 3.) compare these relationships to others in the Colorado River basin for which faunal data already exist, and 4.) determine if potential exists to restore water temperatures in this reach so that rare fish species may benefit. Faunal surveys for adult and young fishes will be conducted throughout the Green River downstream to the Yampa River and perhaps below.. Temperature data will be gathered from published accounts (U.S. Geological Survey, U.S. Fish and ~Idlife Service) and with continuously recording thermographs if necessary. Fish faunal and environmental (mostly temperature) data from the Green River area will be compared to data for other reaches where rare fishes are known to occur. Information from existing collections for the Green River and other river reaches will be used extensively in this analysis. Study #41. Effects of Flow Regulation and Ice on Overwinter Nursery Habitat of Age-0 Colorado squawfish. Study Goals The goal of Study #41 is determine the effect of winter flow regulation and ice formation on habitat availability for young Colorado squawfish. Flaming Gorge Research Program 29