Wash. Rev. Code § 47.04.080
The department is empowered to join financially or otherwise with any other state or any county, city, or town of any other state, or with any foreign country, or any province or district of any foreign country, or with the federal government or any agency thereof, or with any or all thereof, for the erecting, constructing, operating, or maintaining of any bridge, trestle, or any other structure, for the continuation or connection of any state highway across any stream, body of water, gulch, navigable water, swamp, or other topographical formation requiring any such structure and forming a boundary between the state of Washington and any other state or foreign country, and for the purchase or condemnation of right-of-way therefor.
RCW 47.04.080