Provides that a watershed management partnership formed under the authority of RCW 39.34.210 that is composed entirely of public agencies authorized to exercise the power of eminent domain in the manner provided by chapter 8.12 RCW, and a separate legal entity established by such a partnership to conduct the cooperated undertaking of the partnership under the same statutory authority, may also exercise the power of eminent domain as provided in chapter 8.12 RCW; provided that, the authority granted shall be limited to those purposes for which the watershed management partnership was formed.