Water-resources data for the 1991 water year for Massachusetts and Rhode Island consists of stage, discharge, and water quality of streams; contents of lakes and reservoirs; and ground-water levels. This report contains discharge records for 79 gaging stations, month end contents for six lakes and reservoirs, water quality for nine gaging stations, and water levels for119 observation wells. Also included are data for 58 low-flow partial-record stations. Additional water data were collected at various sites, not part of the systematic data-collection program, and are published as miscellaneous measurements. A few pertinent stations in bordering states are also included in this report. These data represent that portion of the National Water Data System operated by the U.S. Geological Survey and cooperating State and Federal agencies in Massachusetts and Rhode Island.