Watershed Boundary Dataset — hydrologic unit boundaries
The federal hierarchy of drainage areas for the United States, Puerto Rico and the US Virgin Islands, from two-digit regions down to sixteen-digit subwatersheds. Each unit has a hydrologic unit code and a name, which is what turns the HUC on a USGS gauge record into a place a reader recognises.
Rights
- Commercial reuse
- Yes
- Redistribution
- Yes
- Derivative use
- Yes
- Attribution required
- No
- Restrictions
- Applies to material authored by US federal agencies. Third-party material carried within a federal product may be separately protected.
- Terms last checked
- 26 August 2026
Access and coverage
- Publisher
- United States Geological Survey / USDA Natural Resources Conservation Service
- Geographic coverage
- United States, Puerto Rico and the US Virgin Islands
- Resolution
- Hydrologic units from 2 to 16 digits; Hydrionis uses the 8-digit subbasin
- Update frequency
- irregular
- Formats
- json, api
- Bulk download
- Available
- Registration required
- No
- Cost to Hydrionis
- Free
- Domains
- river flow
Notes
Used for names, not for geometry. Hydrionis asks this service what an eight-digit hydrologic unit is called and takes the answer; it downloads no polygons and performs no spatial join, so the eight thousand subbasin boundaries never enter the repository. The service states its own terms in its metadata rather than leaving them to be inferred from federal-work status: "Use Constraints: None. All data are open and non-proprietary… Acknowledgment of the U.S. Geological Survey would be appreciated for products derived from these data." Acknowledgement is appreciated rather than required, and Hydrionis gives it anyway. The version in use is the July 2026 refresh, as the service reports it.