Water resources data for the 1978 water year for Pennsylvania consist of records of discharge, and water quality of streams; contents, of lakes and reservoirs; and water levels of ground-water wells. This volume contains records for water discharge at 83 gaging stations; contents at 10 lakes and reservoirs; water quality at 59 gaging stations and water levels at 16 observation wells. Also included are data for 43 crest-stage, 35 low-flow, and 44 water-quality partial-record stations. Locations of these sites not involved in the systematic data-collection program and are published as miscellaneous measurements and analyses. These data together with the data in Volume 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.