Water resources data for the 1990 water year for Mississippi consist of records of stage, discharge, and water quality of streams; stage, and water quality of lakes and reservoirs and water levels and water quality of ground-water wells. This report contains records of water discharge at 78 gaging stations; stage records for 19 of these gaging stations; stage only at 6 gaging stations; water quality for 23 streamflow gaging stations, 2 ungaged stream sites, 3 precipitation quality stations, and 42 wells; and water levels for 244 observation wells. Also included are peak-discharge data for 55 crest-stage partial-record stations, and discharge data at 6 flood hydrograph partial-record stations, and water quality data at 9 partial-record or miscellaneous sites and 96 short-term study sites. Locations of these sites are shown on Figures 4-6, Additional water data were collected at various sites, not part of the systematic data collection program, 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 Mississippi.