The Great Dismal Swamp (the swamp) is a forested peatland in southeastern Virginia and northeastern North Carolina. Since early colonial times, timber harvesting and drainage through a network of ditches constructed to facilitate the harvesting have altered these ecosystems. The U.S. Fish and Wildlife Service has managed the swamp as the Great Dismal Swamp National Wildlife Refuge since 1974 to restore its forest communities to those present in early colonial times. Part of the approach to forest restoration has been to "restore the hydrology." The report by Speiran and Wurster (2020) describes the hydrology and water quality across the swamp. Part of the data used to describe the hydrology and water quality of the Great Dismal Swamp are not available through other publicly accessible databases. These data are derived from three sources: (1) water-quality data collected at 90 sites throughout the swamp by the U.S. Geological Survey and the U.S. Fish and Wildlife Service as part of a one-time synoptic survey on March 15-31, 2016, (2) water-level, flow, and forest-cover data collected across the swamp by the U. S. Fish and Wildlife Service since 2009, and (3) data collected by the U.S. Army Corps of Engineers since 1940 on levels of Lake Drummond and flow from the Feeder Ditch and the Dismal Swamp Canal at Deep Creek, Va., and South Mills, N.C. The water-quality data were used to help identify and verify sources of water to the swamp. Forest-cover data provide a reference for comparison with forest cover in the early 1970s and the future. The remaining data are hydrologic information within and around the swamp. Reference: Speiran, G.K., and Wurster, F.C., 2020, Hydrology and water quality of the Great Dismal Swamp National Wildlife Refuge, Virginia and North Carolina, and implications for hydrologic-management goals and strategies: U.S. Geological Survey Scientific Investigations Report, 2020-XXXX, xx p.