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Federal
National Hydrography Dataset (NHD) - USGS National Map Downloadable Data Collection NGDA
Department of the Interior —
The National Hydrography Dataset (NHD) is a feature-based database that interconnects and uniquely identifies the stream segments or reaches that make up the nation's... -
Federal
EnviroAtlas - HU12_polygon
U.S. Environmental Protection Agency —
This data set is a complete digital hydrologic unit boundary layer to the Subwatershed (12-digit) 6th level for the entire United States. This data set consists of...