The Peconic Estuary Watershed (also known as the Peconic Estuary Study Area) is synonymous with the groundwater contributing area to the Peconic Estuary, delineated by the United States Geological Survey (USGS). The western portion of the watershed, the Peconic River and western Flanders Bay, is a shallow flow subsystem delineated based on work by Kroulikas (USGS - Coram, NY). Chris Schubert (USGS - Coram, NY) delineated the groundwater contributing area to the Peconic Estuary on Long Island's North and South Forks and approved of Kroulikas' earlier work on the western estuary (see supplementary information for citation). This layer was created by the Program Office of the Peconic Estuary Program (SCDHS - Office of Ecology) with the support of the PEP Management Conference. The groundwater contributing area boundary is highly accurate.