The Riparian Zone Mask represents surface water in the United States and its estimated riparian zone. These areas were determined using grid analysis of an approximate 100 meter buffer placed around the combined surface water features of the 2019 National Land Cover Database (NLCD) produced by the Multi-Resolution Land Characteristics Consortium and the 1:100,000 scale National Hydrography Dataset (NHD) Plus version 2.1. Features from NLCD included are 'Open Water' (code 11), 'Woody Wetlands' (code 90) and 'Emergent Herbaceous Wetlands' (code 95). The combination of these two datasets and all cells with a distance of 108 meters or less from surface water are included in the Riparian Zone (RZ). This dataset was produced by the US EPA to support research and online mapping activities related to the Watershed Index Online (WSIO) and EnviroAtlas. 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 each attribute in this dataset can be found in its associated EnviroAtlas Fact Sheet (https://www.epa.gov/enviroatlas/enviroatlas-fact-sheets).