Wash. Rev. Code § 87.03.555
The boundaries of any irrigation district now or hereafter organized under the provisions of this chapter may be changed in the manner herein prescribed, but such change of the boundaries of the district shall not impair or affect its organization, or its rights in or to property, or any of its rights or privileges of whatsoever kind or nature; nor shall it affect, impair or discharge any contract, obligation, lien or charge for or upon which it was or might become liable or chargeable, had such change of its boundaries not been made, except as hereinafter expressly in RCW 87.03.645 prescribed: PROVIDED, That in case contract has been made between the district and the United States, or the state of Washington, as in RCW 87.03.140 provided, no change shall be made in the boundaries of the district, and the board of directors shall make no order changing the boundaries of the district until the secretary of the interior or the director of ecology shall assent thereto in writing and such assent be filed with the board of directors.
RCW 87.03.555
Consolidation of irrigation districts: RCW 87.03.530 through 87.03.551.