Wash. Rev. Code § 88.32.010
Every county in this state is hereby authorized and empowered, by and through its county commissioners, whenever the government of the United States is intending or proposing the construction or operation of any river, lake, canal or harbor improvement, partly or wholly within such county, and whenever said board of county commissioners shall adjudge, upon a petition therefor filed with it and signed by at least one hundred freeholders of said county who each own realty of the assessed valuation of not less than five thousand dollars, situated within the limits of the improvement district sought to be created, that it is for the general benefit and welfare of the people of the county, that such river, lake, canal or harbor improvement be made and completed to define and establish an assessment district within such county and to levy an assessment upon so much of the taxable real estate of such county as shall be specially benefited by such improvement as hereinafter provided, for the purpose of paying the expenses of such improvement, or so much thereof as said board of county commissioners shall determine, not in any instance exceeding one percent of the taxable valuations of all real and personal property in the entire county as appearing on the then last assessment roll. Such improvement shall be known as river and harbor improvement.
RCW 88.32.010
Limitation of levies: RCW 84.52.050 through 84.52.056.