ORS § 539.210
Whenever proceedings are instituted for determination of rights to the use of any water, it shall be the duty of all claimants interested therein to appear and submit proof of their respective claims, at the time and in the manner required by law. Any claimant who fails to appear in the proceedings and submit proof of the claims of the claimant shall be barred and estopped from subsequently asserting any rights theretofore acquired upon the stream or other body of water embraced in the proceedings, and shall be held to have forfeited all rights to the use of the water theretofore claimed by the claimant. Any person interested in the water of any stream upon whom no service of notice has been had of the pendency of proceedings for determination of the rights to the use of water of the stream, and who has had no actual knowledge or notice of the pendency of the proceedings may, at any time prior to the expiration of one year after entry of the determination of the Water Resources Director, file a petition to intervene in the proceedings. The petition shall contain, among other things, all matters required by this chapter of claimants who have been duly served with notice of the proceedings, and also a statement that the intervenor had no actual knowledge or notice of the pendency of the proceedings. Upon the filing of the petition in intervention, the petitioner shall be allowed to intervene upon such terms as may be equitable and thereafter shall have all rights vouchsafed by this chapter to claimants who have been duly served.
ORS 539.210