Wash. Rev. Code § 86.09.160
Flood control districts created under the provisions of this chapter shall have authority to act as fiscal agent or other authority for the United States to make collections of money for or on behalf of the United States or any federal agency thereof in connection with the operations of said district, whereupon said district and the county treasurer for said district shall be authorized to act and to assume the duties and liabilities incident to such action and the district board shall have full power to do any and all things required by any statute now or hereafter enacted in connection therewith and to do all things required by the rules and regulations now or that may hereafter be established by any department or agency of the state or federal government in regard thereto.
RCW 86.09.160