Wash. Rev. Code § 35A.14.210
Decisions of the county annexation review board shall be final unless within ten days from the date of said action a governmental unit affected by the decision or any person owning real property in or residing in the area proposed to be annexed files in the superior court a notice of appeal. The filing of such notice of appeal within such time limit shall stay the effective date of the decision of the board until such time as the appeal shall have been adjudicated or withdrawn. On appeal the superior court shall not take any evidence other than that contained in the record of the hearing before the board. The superior court may affirm the decision of the county annexation review board or remand the case for further proceedings; or the court may reverse the decision and remand if it finds that substantial rights have been prejudiced because the findings, conclusions, or decision of the board are:
RCW 35A.14.210