Water resources data for the 1979 water year for Montana consist of records of stage, discharge, and water quality of streams; stage, contents and water quality of lakes and reservoirs; and water levels in wells. This report contains discharge records for 226 gaging stations; stage only records for 1 lake station; stage/contents for 9 lakes and reservoirs; water quality for 137 stations, 3 lakes, water levels for 23 observation wells. Also included are 172 crest-stage partial-record stations and 43 smaller reservoirs. Additional water data were collected at various sites, not part of the systematic data collection programs, and are published as miscellaneous measurements. 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 Montana.