Puget Sound, deep inlet of the eastern North Pacific indenting northwest Washington state. It stretches south for 100 miles (160 km) from Admiralty Inlet and Whidbey Island (beyond which lie the straits of Georgia and Juan de Fuca). Hood Canal is a large western extension. The sound is the submerged northern end of the Cowlitz-Puget trough (see Pacific Mountain Systems for a visual/geological reference), which extends for some 350 miles (565 km) between the Cascade Range and the Coast Ranges. The southern end of this trough is the Willamette River valley. Many streams enter the sound from the east, of which the Skagit, Snohomish, and Duwamish Waterway are navigable for a portion of their lengths. Puget Sound has many excellent deep water harbors, including Seattle, Tacoma, Everett, and Port Townsend, which serve as outports for rich farmlands along the river estuaries. Bremerton's naval shipyard adds military shipping to the sound's large volume of local and international trade. The sound also serves as the southern terminus of the Inside Passage to Alaska. It provides a sheltered playground for pleasure boats and still yields a salmon catch, though the latter is much reduced from former levels.