Wash. Rev. Code § 36.61.110
No lawsuit may be maintained challenging the jurisdiction or authority of the county legislative authority to proceed with the lake or beach improvement and maintenance activities and creating the lake or beach management district or in any way challenging the validity of the actions or decisions or any proceedings relating to the actions or decisions unless the lawsuit is served and filed no later than forty days after publication of a notice that the ordinance has been adopted ordering the lake or beach improvement and maintenance activities and creating the lake or beach management district. Written notice of the appeal shall be filed with the county legislative authority and clerk of the superior court in the county in which the property is situated.
RCW 36.61.110