RCW 35.13.010: Authority for annexation.

Any portion of a county not incorporated as part of a city or town but lying contiguous thereto may become a part of the city or town by annexation. An area proposed to be annexed to a city or town shall be deemed contiguous thereto even though separated by water or tide or shore lands [tidelands or shorelands] on which no bona fide residence is maintained by any person.