Water-resources data for the 1981 water year for California consists of records of stage, discharge, and water quality of streams; stage and contents in lakes and reservoirs; and water levels and water quality in wells. Volume 4 contains discharge records for 167 gaging stations; stage and contents for 26 lakes and reservoirs; precipitation data for 2 stations; water quality for 17 stations; water levels for 55 observation wells, and water quality for 18 wells. Also included are 4 crest-stage partial-record stations and 7 low-flow partial-record stations. Additional water data are collected at various sites, not part of the systematic data collection program, and are published as special investigations. These data represent that part of the National Water Data System operated by the U.S. Geological Survey and cooperating State and Federal agencies in California.