Wash. Rev. Code § 86.16.010
The legislature finds that the alleviation of recurring flood damages to public and private property and to the public health and safety is a matter of public concern. As an aid in effecting such alleviation the state of Washington, in the exercise of its sovereign and police powers, hereby assumes full regulatory control over the navigable and nonnavigable waters flowing or lying within the borders of the state subject always to the federal control of navigation, to the extent necessary to accomplish the objects of this chapter. In addition, in an effort to alleviate flood damage and expenditures of government funds, the federal government adopted the national flood insurance act of 1968 and subsequently the flood disaster protection act of 1973. The department of ecology is the state agency in Washington responsible for coordinating the floodplain management regulation elements aspects of the national flood insurance program.
RCW 86.16.010