Water resources data for the 1998 water year for Michigan consists of records of stage, discharge, and water quality of streams; stage, contents, and water quality of lakes and reservoirs; and water levels and water quality of groundwater wells. This report contains discharge records for 141 streamflow-gaging stations; stage only records for 1 stream-gaging station and 20 lake-gaging stations; stage and contents for 1 reservoir; water-quality records for 26 streamflow-gaging stations and 1 lake-gaging station; water-level records for 35 ground-water wells. Also included are 31 crest-stage partial-record stations. Additional water data were collected at various sites not involved in the systematic data-collection program. Miscellaneous data were collected at 45 discharge measuring sites and 71 water-quality sampling sites. These data represent that part of the National Water Data System collected by the U.S. Geological Survey and cooperating State, local, and Federal agencies in Michigan.