Hood Canal is a natural, glacier-carved fiord more than 60 miles long, which forms the westernmost waterway and margin of the Puget Sound basin. It is situated in Jefferson, Kitsap, and Mason Counties. It begins in the north in Admiralty Inlet between Tala Point and Foulweather Bluff and extends southwesterly about 45 miles to the Great Bend at Annas Bay. From there its “hook ” extends northeasterly 15 miles to its head at the Union River estuary near Belfair.

The Hood Canal watershed is defined as all the land and waters within the canal's hydrographic boundary- the drainage basin in which all the water flows to the canal. It encompasses a highly interactive system that is dependent upon the continuing cycle of clean water and nutrients to sustain its biological character.