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time. In the Green River, young Colorado squawfish are found in backwaters more often than fish in the San Juan River, and studies have shown that the San Juan River has relatively small amounts of backwaters compared with the Green and Colorado rivers. But the success of the stocked Colorado squawfish in the San Juan River has shown that this system has the habitats necessary for the survival and growth of these young fish. j' Studies assessing the flows needed to build and maintain cobble bars and backwaters similar to those used by Colorado squawfish were an important part of the 7-year research effort. These studies showed that relatively high flows were needed to build and clean these habitats, but that lower flows were needed to make them more abundant at the proper time of the year. During the 7 -year research period, a number of responses to the reregu1ation of Navajo Dam were identified, primarily the release of high spring peak flows. Colorado squawfish young were found in very low numbers, or not at all, during low spring runoff years, and in larger numbers during higher flow years. The young of blue head sucker and speckled dace, two other native species, were found in greater numbers during high flow years compared with low flow years. Ranne1mouth sucker, another native species, tended to decline during the research period, but still remained the most abundant native species in the river. The change to a more-natural hydrograph during the research period resulted in more cobble and less sand habitats in the river, apparently favoring b1uehead sucker and speckled dace rather than flannelmouth sucker. Nonnative fishes in the San Juan River are potential predators and competitors with the native JI..' species and have been implicated in the decline of the native fishes throughout the Colorado River . Basin. Populations of some nonnative fishes changed during the research period, but no major reduction in nonnative fish numbers were documented. Some authors have suggested that nonnative fishes may be reduced by high natural flows, but this was not the case in the San Juan River during the 7-year research period. Contaminants were also studied as a potential1irniting factor for native fishes, but no pattem of contaminant concentrations and flow was found. Table S.1 summarizes the biological and habitat responses that were found during the research period and the flows that were important in producing those responses. FLOW RECOMMENDATION RiverWare, a generic hydrologic model, was used as the primary modeling tool for developing the flow recommendations. The model sirnulates the flow in the river at various gages at different points in time, including the past, present, and future. It does this by incorporating all past, present, and potentially future water development projects into the model. The 1929 to 1993 period of record was used in the model to simulate flows under the various development scenarios. Existing gaging stations were used to calibrate the model to assure it was working properly for historic conditions. The model was completed with input from the Bureau of Reclamation (Bureau), Bureau of Indian Affairs (BIA), and the states of New Mexico and Colorado. SJRIP Biology Committee 16 September 199~ 5-3 Executive Summary Draft Aow Report .