The Snohomish River flows into Possession Sound at Port Gardner Bay.

[2] In 1825 a large piece of the southern tip of Camano Island slid into Possession Sound—an event known as the Great Slide.

A resultant tsunami from the slide drowned many Indian residents of nearby Hat Island.

[3] The Washington State Route 525, Mukilteo-Clinton passenger ferry run crosses the narrowest section of Possession Sound.

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