Wash. Rev. Code § 53.34.120
The state of Washington does hereby covenant and agree with the holders of revenue bonds or notes issued by a district under the authority of this chapter that the state will not limit or alter the rights hereby vested in a district to acquire, maintain, construct, reconstruct, improve, extend, add to, better and operate the projects authorized to be constructed or acquired under the provisions hereof and to establish, collect, and pledge such rates, rentals, tolls, charges, license, and other fees as may be convenient or necessary to produce sufficient revenue to meet the expense of maintenance and operation of such projects and to fulfill the terms of any agreements made with holders of such revenue bonds and notes or in any way impair the rights and remedies of bondholders and noteholders until the bonds or notes together with interest thereon, with interest on any unpaid installments of interest, and all costs and expenses in connection with any action or proceedings by or on behalf of the bondholders or noteholders, are fully met and discharged. The provisions of this chapter and of the resolutions, trust agreements and proceedings authorizing revenue bonds and notes hereunder shall constitute a contract with the holders of said bonds and notes.
RCW 53.34.120