Wash. Rev. Code § 35.23.410
The city council may lease for business purposes portions of the ends of streets terminating in the waterfront or navigable waters of the city with the written consent of all the property owners whose properties abut upon the portion proposed to be leased. The lease may be made for any period not exceeding fifteen years but must provide that at intervals of every five years during the term, the rental to be paid by the lessee shall be readjusted between him or her and the city by mutual agreement, or if they cannot agree by a board of arbitration, one to be chosen by the city, one by the lessee and the third by the other two, their decision to be final. The vote of two-thirds of all the councilmembers elected is necessary to authorize such a lease.
RCW 35.23.410