Wash. Rev. Code § 85.28.140
Any person or persons who may hereafter take a tract of tide land or marsh and shall desire to adopt as his or her boundary line any dike or ditch heretofore constructed upon and entirely within the boundary line of a neighboring contiguous tract he or she may join on to said tract and adopt said dike as his or her boundary by paying to the owner of the tract upon which said dike is constructed one-half of the cost and expense of the construction thereof, and any person so adopting the dike or ditch of another without contributing his or her half share of the cost or expense thereof shall be liable for his or her said half share, which may be recovered in a civil action in any court of competent jurisdiction, or the owner of the dike or ditch so used may secure a lien upon the tract of land bounded by said dike for the amount due for the use of said dike in accordance with the provisions of the law securing a lien to material suppliers and mechanics: PROVIDED ALWAYS, That when such dike has become the common boundary of two adjacent tracts, it shall be and remain the common boundary and the persons owning the said tracts shall be mutually liable for the expense of keeping it in repair, share and share alike.
RCW 85.28.140
Intent-Finding-2007 c 218: See note following RCW 41.08.020.