A water balance prepared for the Emerald Lake basin illustrates the absolute and relative magnitudes of the main water transfers in this alpine catchment in the Sierra Nevada over two water years. The water balance over both years, expressed as equivalent water depths averaged over the catchment area, was total precipitation (3670 mm)— total losses in the atmosphere (800 mm) = total streamflow (2830 mm) + residual (40 mm). Snow dominated the water balance during the study period, accounting for 95% of the precipitation. The spring snowmelt periods accounted for more than 85% of the annual streamflow and were followed by long recessions through summer, autumn, and winter. Estimated total evaporation from snow, water surfaces, soil, and vegetation at Emerald Lake was 22% of the estimated precipitation. Evaporation from snow was the principal water loss to the atmosphere, accounting for about 80% of the total evaporation. Actual evapotranspiration estimated over 15 non winter months was less than 4% of the precipitation during the two water years. Groundwater storage and release accounted for only a small portion of the total quantity of water in the annual water balance of this largely impermeable basin.