Wash. Rev. Code § 87.03.150
The title to all property acquired under the provisions of this chapter shall immediately, and by operation of law, vest in such irrigation district and shall be held by such district in trust for, and is hereby dedicated and set apart to the uses and purposes set forth in this chapter; and said board is hereby authorized and empowered to hold, use, acquire, manage, occupy and possess said property as herein provided: PROVIDED, HOWEVER, That any property so acquired by the district may be conveyed to the United States, or the state of Washington, insofar as the same may be for the benefit of the district under any contract that may be entered into with the United States, or the state of Washington, pursuant to this act.
The title acquired by an irrigation district under the provisions of this act shall be the fee simple title or such lesser estate as shall be designated in the decree of appropriation.
RCW 87.03.150
Board's powers and duties (contracts with state or United States): RCW 87.03.140.