Water resources data for the 1986 water year for Pennsylvania consist of records of discharge and water quality of streams; contents and elevations of lakes and reservoirs; and water levels and water quality of ground-water wells. This report, Volume 1, includes records from the Delaware River basins. Specifically, it contains: (1) Discharge records for 74 continuous record streamflow-gaging stations and 72 partial-record stations; (2) elevation and contents records for 12 lakes and reservoirs and elevations for 4 tidal stations; (3) water-quality records for 40 streamflow-gaging stations, for 43 ungaged streamsites, and (4) water-level records for 17 observation wells. Locations of these sites are shown on figures 6-9. Additional water data were collected at various sites not involved in the systematic data-collection program and are published as miscellaneous measurements and analyses. These data together with the data in Volumes 2 and 3, represent that part of the National Water Data System operated by the U.S. Geological Survey and cooperating State, local, and Federal agencies in Pennsylvania.