Wash. Rev. Code § 53.34.160
It is found, determined, and declared that the creation and establishment of projects authorized by this chapter are in all respects for the benefit of the people of the state of Washington, for the improvement of their welfare and prosperity, and for the promotion of intrastate, interstate, and foreign commerce, the transportation of freight, commercial, and passenger traffic, is a public purpose, that such projects operated by port districts are essential parts of the public transportation system, and that such districts will be performing essential governmental functions in the exercise of the powers conferred upon them by this chapter; and the state of Washington covenants with the holders of revenue bonds and notes that port districts shall not be required to pay any taxes or assessments, or other governmental charges in lieu thereof, upon any of the property acquired by them or under their respective jurisdictions, control, possession, or supervision, upon the activities of port districts in the operation and maintenance of such projects, or upon any charges, fees, rentals, revenues, or other income received by such districts from such projects and that the revenue bonds and notes of port districts and the income therefrom shall at all times be exempt from all taxation in the state of Washington, except transfer, inheritance, and estate taxes. This section shall constitute a covenant and agreement with the holders of all revenue bonds and notes issued by port districts pursuant to the provisions of this chapter.
RCW 53.34.160