This EnviroAtlas web service contains layers depicting hydrologic unit boundary layers and labels for the Subregion level (4-digit HUCs), Subbasin level (8-digit HUCs), and Subwatershed level (12-digit HUCs) for the conterminous United States. EnviroAtlas (https://www.epa.gov/enviroatlas) allows the user to interact with a web-based, easy-to-use, mapping application to view and analyze multiple ecosystem services for the contiguous United States. The dataset is available as downloadable data (https://edg.epa.gov/data/Public/ORD/EnviroAtlas) or as an EnviroAtlas map service. Additional descriptive information about this dataset can be found in its associated EnviroAtlas Fact Sheet (https://www.epa.gov/enviroatlas/enviroatlas-fact-sheets).