Water resources data for the 1991 water year for Idaho consist of records ofstage, discharge, and water quality of streams; stage, contents, and water qualityof lakes and reservoirs; discharge of irrigation diversions; and water levels andwater quality of ground water. The two volumes of this report contain dischargerecords for 197 stream-gaging stations and 38 irrigation diversions; stage onlyrecords for 6 stream-gaging stations; stage only for 7 lakes and reservoirs;contents only for 23 lakes and reservoirs; water-quality for 50 stream-gagingstations, 400 wells, and 11 lakes; daily totals for 1 precipitation gage; andwater levels for 475 observation wells. Additional water data were collected atvarious sites not involved in the systematic data collection program and arepublished as miscellaneous measurements. These data represent that part of theNational Water Data System operated by the U.S. Geological Survey and cooperatingState and Federal Agencies in Idaho, adjacent States, and Canada.