Water resources data for the 1990 water year for Michigan consists of records of stage, discharge, and water quality of streams; stage and contents of lakes and reservoirs; and water levels and water temperature of ground water. This report contains discharge records for 146 streamflow-gaging stations; stage only records for 1 river-gaging station and 13 lake-gaging stations; stage and contents for 5 lakes and reservoirs; water-quality records for 22 streamflow-gaging stations; water-level records for 51 observation wells; and water-temperature records for 5 observation wells. Also included are 46 crest-stage partial-record stations and 8 low-flow partial-record stations. Additional water data were collected at various sites not involved in the systematic data-collection program. Miscellaneous data were collected at 63 measuring sites and 22 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.