Water resources data for the 1977 water year for Maryland and Delaware consist of records of stage, discharge, and water quality of streams; stage, contents, and water quality of lakes and reservoirs; and water levels and water quality of ground water. This report contains discharge records for 107 gaging stations; stage and contents for 1 reservoir; water quality for 53 gaging stations and 37 wells; and water levels for 29 observation wells. Also included are data for 87 low-flow partial-record stations, 19 crest-stage partial-record stations, and 4 tidal crest-stage partial-record stations. These data represent that part of the National Water Data System collected by the U.S. Geological Survey and cooperating State and Federal agencies in Maryland and Delaware.