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Federal
EnviroAtlas - NHDPlus V2 Hydrologic Unit Boundaries Web Service - Conterminous United States
U.S. Environmental Protection Agency —
This EnviroAtlas web service contains layers depicting hydrologic unit boundary layers and labels for the Subregion level (4-digit HUCs), Subbasin level (8-digit... -
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...