The Nooksack River watershed spans part of the border between British Columbia and the State of Washington. In August 2018, the international, multi-agency Nooksack River Transboundary Technical Collaboration Group was established to implement a three-year work plan to reduce fecal bacteria concentrations in the Nooksack River watershed. As a work plan deliverable, the group produced this annual report summarizing first year project activities.

The watersheds of Washington’s San Juan Islands were thought to be too small to support wild salmonid populations, and many streams flow only seasonally. But a 2019 article in the journal Conservation Genetics reports that at least five watersheds in the region support populations of coastal cutthroat trout (Oncorhynchus clarki clarki). Genetic analysis of the cutthroat trout in three of the watersheds suggest two support native populations. The findings are important for understanding the conservation status of these previously unknown populations. 

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.

The Washington State Department of Ecology and other state natural resources agencies have divided the Washington into 62 "Water Resource Inventory Areas" or "WRIAs" to delineate the state's major watersheds.