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chia and Bergersen (1986) estimated production (2.2 and 3.6 g_m-2 in 1979 and 1980, respectively) of Colorado River cutthroat trout in a headwater tributary of the Colorado River and concluded that biomass and production were dependent on stream-specific physical properties. The Endangered Species Act of 1973 mandated efforts to maintain rare native fishes and their habitats in the Colorado basin. Listing of fishes stimulated studies of their basic biol- ogy. Information on distribution and relative abundance of fishes in the Upper Colorado River System was compiled by Tyus et al. (1982). Behnke et al. (1982) provided sup- plemental information on fishes of the Green and Upper Mainstem Colorado sub-basins. Recent reports on fishes of the Colorado River System have concentrated on reproduction (Morgensen 1983; McAda and Wydoski 1983, 1985; Nesler et al. 1988), early life history (Haynes et al. 1984), marking (Muth et al. 1988), life-history strategies (Constantz 1979, 1981), foods and feeding (Barber and Minckley 1983; Marsh 1987), artificial propagation (Hamman 1985a, 1985b, 1986; Berry 1984; Muth et al. 1985), and conserving genetic diversity (Vrijenhoek et al. 1985). Culture efforts have focused on preservation of genetic material of rare fishes, description of early life stages (sensu Snyder 1981), or reintroduction of extirpated fishes within their native ranges (Minckley 1983; Johnson 1985). Migrations of Colorado squawfish to restricted upper-basin spawning grounds have been documented (Tyus and McAda 1984; Tyus 1985; Haynes and Bennett 1986). Other reports relate to responses of native fishes to temperature changes (Bulkley and Pimentel 1983; Ihnat and Bulkley 1984; Black and Bulkley 1985a, 1985b; Marsh 1985) and toxic retorted oil shale (Woodward et al. 1985) associated with dams and energy development, respectively. Amin (1968), Marsh and Rinne (1983), and Haynes and Muth (1985) noted fish spinal deformities which may be associated with altered ecosystems. Much informa- tion on upper-basin fishes has resulted from field studies through the Colorado River Fisheries Project (Miller et al, 1982b-d), while emphasis in the lower basin has been on acquisition of habitats and brood stocks, production, and reintroduction (Johnson and Rinne 1982; Johnson 1985). Recovery of native Colorado River fishes is the responsi- bility of the U. S. Fish and Wildlife Service. The Recovery Implementation Task Group of the Upper Colorado River Basin Coordinating Committee and an ad hoc recovery team for lower basin fishes spearhead recovery efforts, A Desert Fishes Recovery Team deals with native species of North American deserts within the basin. Since 1935, riparian vegetation along Colorado basin streams has been modified by water management, grazing of cattle, competitive interactions involving tamarisk, and phreatophyte removal to conserve groundwater (Ohmart et al. 1977; Brown et al. 1977; Graf 1985; Stanford and Ward 1986a). Tamarisk has competed effectively with native riparian plants since its appearance on the Salt River near Phoenix in the 1890s. It has spread northward at an average rate of 20 km-ycl (Graf 1985) and is becoming estab- lished on beaches along the lower Yampa River (Haynes and Bennett (1986). It has had greatest impact in the central and lower portions of the basin, where it occurs in dense thickets which have replaced willows and cottonwoods on sandbars and banks. Stream regulation has favored tamarisk expan- sion along fluctuating reservoir shorelines. Ill-advised efforts to salvage water through phreatophyte control have occurred in the Colorado River Basin, and millions of dol- lars have been spent on such clearing projects in the south- western United States over the past 40 yr (Graf 1985). Ohmart et al. (1977) observed that cottonwood commu- nities along the lower Colorado River have been reduced to a precarious state, Only about 1 130 ha of cottonwood- willow communities remain, and less than 202 ha can be considered pure cottonwood communities. Regulated outflows from high dams may create more favorable environments for riparian vegetation (Turner and Karpiscak 1980). Below Glen Canyon Dam, woody plants unable to withstand yearly inundation or grow on unstable substrates are colonizing previously inhospitable river banks (Carothers and Johnson 1983). New strips of woody vegetation extending from Glen Canyon Dam to Lake Mead grow on sediments of unknown stability deposited before construction of Glen Canyon Dam; the wildlife they support are an unexpected benefit from regulation (Carothers and Johnson 1983). A post-dam ecological equilibrium has not been achieved along the Colorado River in Grand Canyon, and establishment of a stable riparian community may require decades (Turner and Karpiscak 1980). Recommendations for the Future The future for the Colorado River is certain to be replete with conflicts. Coats (1984) observed that basin water is overappropriated, and there are no immediate prospects of importations from other basins. Therefore, new consump- tive water uses must take water from existing ones. Con- flicts will intensify between wilderness values and instream water uses, agriculture and other uses, and economic effi- ciency and social equity. Future shocks to the system, such as prolonged drought, energy crisis, establishment of native American water entitlements, or large-scale sales of water across state boundaries could exacerbate conflicts (White 1986). Potential solutions include importation of new water supplies (study is prohibited until 1988 by Central Arizona Project legislation), market pricing of water, managing groundwater and surface water as a single system, implementing water conservation technologies, and renegotiating the Colorado River Compact to remedy mis- takes concerning river discharge and disincentives for con- servation in the upper basin (Coats 1984; White 1986). Parts of the Colorado River System might be added to the Wild and Scenic River System and responsibilities of the Bureau of Reclamation broadened to include such social goals as water conservation and in stream use protection. We consider conflicts between development and natural ecosystems paramount and find it difficult to be optimistic about the remaining natural elements of the Colorado River. All agencies working toward recovery of rare native fishes of the Colorado River System have established goals and priorities for research and management. There is need for further biological research (emphasizing threatened and endangered fishes) on population dynamics, homing mechanisms, interactions involving native and non-native species, habitat requirements of all life-history stages, responses to potential water-quality modifications, and potential value of management strategies. Monitoring schemes to routinely assess the status of threatened and endangered fishes should be developed for use by basin- 233