Puget Sound only Puget Sound proper but also for waters to the north, such as Bellingham Bay and the San Juan Islands region. The term "Puget Sound" is used not just for the body of water but also the Puget Sound region centered on the sound. Major cities on the sound include Seattle, Tacoma, Olympia, and Everett, Washington. Puget Sound is also the third largest estuary in the United States, after Chesapeake Bay in Maryland and Virginia, and San Francisco Bay in northern California. In 1792 George Vancouver gave the name "Puget's Sound" to the waters south of the Tacoma Narrows, in
Puget Sound Central Basin. Puget Sound's sills, a kind of submarine terminal moraine, separate the basins from one another, and Puget Sound from the Strait of Juan de Fuca. Three sills are particularly significant—the one at Admiralty Inlet which checks the flow of water between the Strait of Juan de Fuca and Puget Sound, the one at the entrance to Hood Canal (about below the surface), and the one at the Tacoma Narrows (about ). Other sills that present less of a barrier include the ones at Blake Island, Agate Pass, Rich Passage, and Hammersley Inlet. The depth of the basins is