Wash. Rev. Code § 85.08.300
The board of supervisors of the district shall consist of three elected supervisors. The initial supervisors shall be appointed, and the first elected supervisor elected, as provided in chapter 85.38 RCW. The board of supervisors shall have charge of the construction and maintenance of the systems of improvements, subject to the limitations hereinafter set forth, and may employ a superintendent of construction and maintenance who may be one of the two elected supervisors. The supervisors may be employed upon the construction or maintenance, receiving the same compensation as other labor of like character.
When a district contains not more than five hundred acres, or when a petition is presented to the county legislative authority signed by the owners of fifty percent of the acreage of the district praying for such action, the county engineer shall act as the sole supervisor of the district; and in such case the allowance of all claims against the district shall be by the county legislative authority.
RCW 85.08.300