Wash. Rev. Code § 53.25.190
All port districts of the state of Washington which have created or may hereafter create industrial development districts in the manner provided by law, in addition to all powers possessed by such port districts, be and are hereby granted power of eminent domain to acquire real property within the limits of such industrial development district which property is marginal lands as the term is herein defined. The exercise of the power granted in this section shall be exercised in the same manner and by the same procedure as in or may be provided by law for cities of the first class except insofar as such duties may be inconsistent with the provisions of this chapter and the duties devolving upon the city treasurer under said law be and the same are hereby imposed upon the county treasurer for the purposes of this chapter.
RCW 53.25.190
Eminent domain: State Constitution Art. 1 s 16 (Amendment 9).
Eminent domain by cities: Chapter 8.12 RCW.