Mean annual water yields, estimated using a water-budget method, for the upper Big Wood River basin above Glendale Road and for Trail Creek, Warm Springs Creek, and East Fork Big Wood River, Idaho were 410,000, 50,000, 60,000 and 50,000 acre-ft, respectively. Yields also were estimated for 1986 and 1987 water years when data were collected for comparison with long-term average values. During 1986, yields estimated for upper Big Wood River basin, Trail Creek, Warm Springs Creek, and East Fork Big Wood were 580,000, 61,000, 83,000 and 60,000 acre-ft, respectively. During 1987, yields estimated for the respective basins were 230,000, 26,000, 32,000 and 28,000 acre-ft. Availability of surface and groundwater varies seasonally; the greatest quantity is available during spring snowmelt, and the least is available during mid-winter to late winter. Nutrient concentrations in sampled ground and surface water were near or below detection levels throughout the basin, which indicates that water quality has not been impaired by increased development. Fluoride concentrations were elevated in Warm Springs Creek, probably due to inflow of thermal water.