Port Susan is a bay and strait located in the U.S. state of Washington. Part of the Whidbey Island Basin of Puget Sound, Port Susan is bounded by Camano Island to the west and the mainland to the east. The Stillaguamish River empties into the northern end of Port Susan. To the south, Port Susan connects with the rest of Puget Sound via Possession Sound and Saratoga Passage. A swampy waterway connects the northern end of Port Susan with Skagit Bay.