Wash. Rev. Code § 85.24.260
The districts organized under the provisions of this chapter, and the commissioners appointed and qualified as such shall have the right of eminent domain with the power by and through the board of commissioners to condemn and cause to be condemned and appropriated private property for the use of said district in the construction and maintenance of the system of dikes, drains, flood dams and drift barriers, and for any other purpose proper, necessary and convenient for the purpose of carrying into effect the powers vested in said district and the commissioners thereof; and that the property of private corporations shall be subject to the same rights of eminent domain as private individuals. Said board of commissioners shall also have the power to acquire by purchase, in the name of the district, any and all real property necessary to make the improvements herein provided for.
RCW 85.24.260