Water Resource Inventory Areas (WRIA) were formalized under Washington Administrative Code (WAC) 173-500-040 and authorized under the Water Resources Act of 1971, Revised Code of Washington (RCW) 90.54. Ecology was given responsibility for the development and management of these administrative and planning boundaries. These boundaries represent the administrative under pinning of this agency’s business activities. The original WRIA boundary agreements and judgments were reached jointly by Washington's natural resource agencies Ecology, Department of Natural Resources, and Washington Department of Fish and Wildlife in 1970 and were updated in 1998 and 2000.
--Source: Department of Ecology
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.