ORS § 539.100
Any person owning any irrigation works, or claiming any interest in the stream involved in the determination shall be a party to, and bound by, the adjudication. Any party who desires to contest any of the rights of the persons who have submitted their evidence to the Water Resources Director as provided in ORS 539.021 to 539.090 shall, within 15 days after the expiration of the period fixed in the notice for public inspection, or within such extension of the period, not exceeding 20 days, as the director may allow, notify the director in writing, stating with reasonable certainty the grounds of the proposed contest, which statement shall be verified by the affidavit of the contestant, the agent or attorney of the contestant. A party not claiming an undetermined vested right under this chapter or not contesting the claim of another need not participate further in the proceeding, nor be served with further notices or documents regarding the adjudication. Upon the filing of a statement of contest, service thereof shall be made by the contestant upon the contestee by mailing a copy by registered mail or by certified mail, return receipt requested, addressed to the contestee or to the authorized agent or attorney of the contestee at the post-office address of the contestee as stated in the statement and proof of claim of the contestee. Proof of service shall be made and filed with the Water Resources Department by the contestant as soon as possible after serving the copy of statement of contest.
ORS 539.100