Puget Sound watershed hydrologic units

There are many ways of defining the boundaries of the Puget Sound watershed. Hydrologic unit codes (HUCs) are nationally standardized divisions that are often used by conservation agencies and national organizations.

In the mid-1970s, the USGS developed a system for subdividing the country into a series of hydrologic units (HU), which identify drainage basins across the country. The units are coded according to four nested levels: Regions, Subregions, Basins (formerly Accounting Units), and Subbasins (formerly Cataloging Units). Each level has two digits, and the aggregated code of 8 digits makes up the complete hydrologic unit code (HUC).

map showing the 21 watershed sub-basins in Puget Sound

Strait of Georgia watershedSan Juan Islands WatershedDungeness-Elwha WatershedCrescent Hoko WatershedHood Canal WatershedSkokomish WatershedPuget Sound WatershedNooksack WatershedFraser WatershedUpper Skagit WwatershedLower Skagit WatershedStillaguamish WatershedSnohomish WatershedSkykomish WatershedSnoqualmie WatershedLake Washington WatershedDuwamish WatershedPuyallup WatershedNisqually WatershedDeschutes Watershed

The 8-digit divisions proved too large for some conservation purposes. In the early 1980s, the Natural Resource Conservation Service (NRCS) mapped 10-digit units onto state maps in order to make the HUC categories more useful for natural resource planning efforts. In the 1990s, the NRCS and State agencies worked towards making 10- and 12-digit units that matched standards for national map accuracy, and in 1992 the NRCS developed a standardized criterion for determining HUs.

Every HU is based only on hydrologic principles. Boundaries are intended to be simple and consistent, without favoring any agency or project. In general, each unit is subdivided into between 5 and 15 smaller units. Hydrologic units are not always synonymous with watersheds, as boundary lines may not include the entire area contributing water to a single outlet.

The Puget Sound subregion (1711) contains areas draining into Puget Sound, the Strait of Georgia, the Fraser River, and the Strait of Juan de Fuca. In Washington State, some agencies also use Water Resource Inventory Areas (WRIAs), established in 1970 by the Department of Ecology, the Department of Fish and Wildlife, and the Department of Natural Resources.

The Watershed Boundary Dataset (WBD) contains all levels of HUCs (1-6) and is consistent across the country. Get data from the Watershed Boundary Dataset (WBD).

Read the Washington State Legislature's definition of Puget Sound waters.

Find articles, maps, and other content tagged by any of the 21 watershed sub-basins in the Puget Sound area.

See how HUCs were used by the USGS and EoPS to determine terrestrial vertebrate species of the Puget Sound watershed. 

Sources: USGS, NRCS