The Salish Sea is the intricate network of coastal waterways located between the south-western tip of the Canadian province of British Columbia, and the north-western tip the U.S. state of Washington. Its major bodies of water are the Strait of Georgia, the Strait of Juan de Fuca, and Puget Sound. It reaches from Desolation Sound at the north end of the Strait of Georgia to Oakland Bay at the head of Hammersley Inlet at the south end of Puget Sound. The inland waterways of the Salish Sea are partially separated from the open Pacific Ocean (a pelagic zone) by Vancouver Island and the Olympic Peninsula, and are thus partially shielded from Pacific Ocean storms. Major port cities on the Salish Sea include Seattle, Vancouver, Tacoma, Bellingham, and Victoria.

The Salish Sea includes the Strait of Juan de Fuca, Strait of Georgia, and Puget Sound, and all their connecting channels and adjoining waters, such as Haro Strait, Rosario Strait, Bellingham Bay, and the waters around and between the San Juan Islands in the U.S. state of Washington and the Gulf Islands in British Columbia, Canada. The western boundary is the entrance to the Strait of Juan de Fuca, defined as a line between Cape Flattery and Carmanah Point. The southern boundary is the southern end of Puget Sound. The northern boundary reaches just beyond the northern end of the Strait of Georgia to include waters that experience the floodstream or tidal surge from the south: Discovery Passage south of Seymour Narrows, Sutil Channel south of Penn Islands, Lewis Channel (between Cortes and West Redonda Island), Waddington Channel (between West Redonda and East Redonda Island), and Pendrell Sound, Desolation Sound, and the southern portion of Homfray Channel (between East Redonda Island and the mainland). These boundaries were based on the 2002 "Georgia Basin–Puget Sound Ecosystem Indicators Report". The total extent of the Salish Sea is about 18,000 square kilometres (6,900 sq mi).