River flows in California are about half normal volumes, and a water shortage could threaten the orange crop in the San Joaquin Valley, federal and state officials said. The lower water figures for California were calculated from measurements of the dwindling snowpack in the Sierra Nevada. The measurements by a 50-agency conglomerate known as the California Cooperative Snow Surveys found little snow left. Statewide, California river flows will average 55% of normal, said Bill Helms, a spokesman for the state Department of Water Resources. In the Fresno area, hundreds of farmers and dozens of water districts that depend on Friant Reservoir on the San Joaquin River will get only about one-third of the water they expected this year, the bureau announced. The river flows are the lowest since the drought year of 1977, Helms said. But they will not cause another general drought because California has a bountiful supply of water in its 1,200 reservoirs.