By October 1, 2001, the department of ecology shall complete a final nonproject environmental impact statement that evaluates streamflows to meet the alternative goals of maintaining, preserving, or enhancing instream resources and the technically defensible methodologies for determining these streamflows. Planning units and state agencies assessing and setting or amending instream flows must, as a minimum, consider the goals and methodologies addressed in the nonproject environmental impact statement. A planning unit or state agency may assess, set, or amend instream flows in a manner that varies from the final nonproject environmental impact statement if consistent with applicable instream flow laws.