The National Hydrography Dataset (NHD) is a digital database of surface water features used to make maps.
It is a digital vector geospatial dataset designed for use in geographic information systems (GIS) to analyze the flow of water throughout the nation.
Using the basic water features, flow network, linked information, and other characteristics, it is possible to study cause and effect relationships, such as how a source of poor water quality upstream might affect a fish population downstream.
The NHD is also linked with similar datasets representing the surface water for Canada and Mexico.
A version of the NHD called the NHDPlus is integrated with elevation and other landscape data to create detailed drainage catchments and flow volume and velocity estimates for streams and rivers of the U.S. at 1:100,000-scale.