(1) The Walla Walla water 2050 plan must be used as an integrated water resource strategy, through a coordinated effort between the states of Washington and Oregon, affected federally recognized tribes, affected federal, state, and local agencies, and agricultural, environmental, business, and other community stakeholders.

(2) In developing water supply solutions in the Walla Walla river basin, the department of ecology should employ an integrated water resource management strategy that will provide concurrent water supply benefits to both instream and out-of-stream uses and address a variety of water resource and ecosystem challenges affecting fish passage, habitat functions, and agricultural, municipal, industrial, and domestic water supply, consistent with the Walla Walla water 2050 plan.

(3) The department of ecology shall consider any increase in the quantity of water supply due to a project being implemented under the Walla Walla water 2050 plan that is completed after July 23, 2023, to be water supply developed under this section.

(4) In implementing subsection (2) of this section, the department of ecology will be advised by the Walla Walla basin advisory committee, including representatives from a broad range of interests, including agricultural, environmental, and other stakeholders, and tribal, local, state, and federal governments.

(5) In consultation with affected federally recognized tribes, the department of ecology shall evaluate the development of a bistate legal regulatory framework for allocation of developed water resources, in collaboration with the state of Oregon.

(6) The department of ecology shall submit a report to the relevant committees of the legislature by June 30, 2025, with a recommendation for the bistate legal regulatory framework necessary for equitable allocation and management of developed water resources from the build out of water supply projects envisioned in the Walla Walla water 2050 plan.

(7) Subject to the availability of amounts appropriated for this specific purpose, the department of ecology is authorized to fund the development, construction, and implementation of projects to implement the Walla Walla water 2050 plan that may be located outside of the state, provided that the projects benefit instream and out-of-stream water demands in the state.

(8) Water supplies developed under this section must be apportioned between the states consistent with any written agreements entered into with the state of Oregon and the confederated tribes of the Umatilla Indian reservation related to the management of water in the Walla Walla river basin.

(9) The department of ecology has the authority to designate water supplies developed under this section for instream flow purposes and placed into the trust water rights program authorized under chapter 90.42 RCW. Water supplies developed under this section that are designated for instream flow purposes are unavailable to satisfy existing water rights, including water rights with superior priority, and are exempt from provisions under RCW 90.42.070.

(10) Water supplies developed under this section must be managed consistent with the intent of the specific project being implemented.

(11) It is the intent of the legislature for the state to share in the cost to implement the Walla Walla water 2050 plan authorized under this section, subject to the availability of amounts appropriated for this specific purpose, with at least one-half of the total costs to finance the implementation of the Walla Walla water 2050 plan funded through federal, private, and other nonstate sources, including private funding sources from entities that benefit from projects. This section applies to the total costs of the Walla Walla water 2050 plan and not to individual projects within the plan and includes funding for projects that have been completed prior to July 23, 2023.

(12) Nothing in this section prevents the department of ecology from regulating water users consistent with existing adjudications to ensure that water use by holders of adjudicated surface water right certificates are not impaired by use under junior groundwater right certificates, claims, and permits.