Along the Canada-United States boundary between Vancouver Island, British Columbia and the San Juan Islands, Washington, and connecting the Strait of Juan de Fuca and Boundary Pass; The S end is formed by a line between Seabird Point (Discovery Island), British Columbia and Cattle Point (San Juan Island), Washington; The W boundary is formed by a line extending from the N shore of Discovey Island through Chatham Island to Cadboro Point (Vancouver Island); the N boundary is formed by a line from the N tip of Assnich Peninsula (Vancouver Island) through Harry Point (Piers Island) to Kanaka Bluff (Portland Island) and then from the N tip of Portland Island to Reynard Point (Moresby Island) and from Point Fairfax (Moresby Island), British Columbia, to Turn Point (Stuart Island), Washington; the E boundary is formed by a line extending from the S tip of Stuart Island to McCracken Point (Henry Island) to Mitchell Bay (San Juan Island).
Named Canal de Lopez de Haro by the Spanish explorer Manuel Quimper in 1790 in hnor of his sailing master.