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reservoirs associated with these diversions are included in export figures. Exports during 1975 accounted for about 19 percent of total water loss (Table 1.2). Perhaps the oldest diversions in the upper Colorado River basin are those associated with the Strawberry Project in northeastern Utah (La Rue 1916). Water was first diverted from the Strawberry River to Hobble Creek in 1893. This diversion is still in operation. Variation in the volume of water exported is large; however, the net increase has been dramatic since 1953 (Figure 1.3). Water exported from the upper basin remained under 150,000 acre-feet until 1938. By 1957, 42 transmountain diversions were exporting about 468,400 acre-feet. Water exports in 1971 totaled 583,000 acre-feet and then rose to 711,000 acre- feet in 1975. Except for the period between 1914 and 1935, exports from the Upper Main Stem have greatly exceeded those of the other subregions (Figure 1.3). In 1975, transmountain exports accounted for 33 percent of the water consumed in the Upper Main Stem Subregion, and only 10 percent and eight percent of the water used in the Green River and San Juan-Colo- rado Subregions, respectively (Table 1.2). Water diverted from the upper Colorado River basin is used in the Great Basin, Arkansas River basin, Platte River basin, and Rio Grande basin. One small diversion in southern Utah imports about 2,600 acre- feet of water annually from the East Fork of the Sevier River into the upper Colorado River basin. Reservoir Evaporation The volume of water lost from the upper basin as a result of evapo- ration from large surface reservoirs has been computed only for the large main stem impoundments. The majority of these reservoirs were formed as a result of the Colorado River Storage Project, authorized by Congress on April 11, 1956. This included construction of six large dams (Table 1.3), most of which were impounding water by 1964 (U.S. Department of Interior 1977). A storage capacity of 33,439,000 acre-feet was developed by 1965, including Lake Powell on the Colorado River, Flaming Gorge and Fontenelle Reservoirs on the Green River, Navajo Reservoir on the San Juan River, 14