This is an appeal from an administrative order that declared about a 270-square-mile portion of northeastern Oregon to be a "critical ground water area” and imposed various restrictions, such as a moratorium on constructing new irrigation wells and limiting removal of water from existing irrigation wells. The dispositive issue is whether the proceedings were initiated with proper notice to persons affected by the restrictions imposed.
The Ground Water Act of 1955 provides that the Water Resources Department may, following a mandatory public hearing, ORS 537.730(2),1 declare that a critical ground water area exists, ORS 537.730(1),2 *246and order corrective measures, ORS 537.735(3).3 Persons who might be affected by such an order must be notified of the public hearing.
The dispute centers on the manner that should be used to convey notice. The Water Resources Department sent written notice by ordinary mail, and argues that is all that is required. Those challenging the *247Department’s order argue that registered or certified mail should have been used.
The relevant statutes contain some support for both positions. The Ground Water Act of 1955 states:
"* * * Written notice of the hearing * * * to each person or public agency known to the director [of the Water Resources Department] from an examination of the records in his office to be a claimant or appropriator of ground water in the area in question * * ORS 537.730(2).
"* * * [T]he hearing * * * procedure shall be such as to secure a full, fair and orderly proceeding and to permit all relevant evidence to be received.” ORS 537.730(3).
These statutes do not require notification by registered or certified mail unless it is implicit in the guarantee of a fair proceeding.
The Water Resources Department is also subject to the Administrative Procedures Act, ORS ch 183, which requires:
"In a contested case, all parties shall be afforded an opportunity for hearing after reasonable notice, served personally or by registered or certified mail.” ORS 183.415(1).
Contested cases include agency proceedings in which individual legal rights are required by statute to be determined only after agency hearing where the individual has a right to be heard and proceedings where the agency has discretion to revoke a right or privilege of a person. ORS 183.310(2)(a) and (b).
The agency proceeding contemplated by the Ground Water Act of 1955 to determine a critical ground water area is a contested case within this meaning because a statute requires a hearing and grants the right to be heard, ORS 537.730(2) and (3), and because the agency has discretion to revoke rights to appropriate water, ORS 537.735(3). Therefore, the Administrative Procedures Act notification rule — registered or certified mail — should have been followed to initiate this proceeding.
*248Were there a conflict between the procedures of the Ground Water Act and the Administrative Procedures Act, the preference would be to follow the APA to promote uniformity. See School Dist. No. 48 v. Fair Dis. App. Bd., 14 Or App 35, 512 P2d 799 (1973). But here there is no conflict; one statute’s requirement (written notice) is merely supplemented by the other statute’s requirement (by certified or registered mail). This is an even stronger case for following the APA than is School Dist. No. 48,
Stroh v. SAIF, 261 Or 117, 492 P2d 472 (1972), does not support respondent’s position. Stroh holds that ordinary-mail notice is sufficient, even when a statute requires something more, when it is conceded the notice was received. Instead of supporting the Water Resources Department, Stroh is actually adverse authority because we have no evidence in this case about whether the ordinary-mail notice was received.
We know from the record that many persons were sent ordinary-mail notice. The record also discloses that many of those same persons did not participate in the hearing. It may be that the nonparticipants received the notice but chose not to attend the hearing, although the stakes were high for farmers irrigating hundreds of acres from thousand-foot-deep wells. But it is equally possible that the nonparticipants never received notice. It is impossible to know.
The final issue is prejudice. All of the petitioners in this court did attend and participate in the hearing that culminated in the order they challenge. Can these petitioners assert the lack of proper notice to persons other than themselves?
In the context of this specific case, we conclude they can. The pattern in the Ground Water Act of 1955 is that all persons who might be affected by restrictions on their appropriation of water should have the opportunity to participate in a hearing to determine a critical ground water area. It is conceivable that other *249water appropriators might, if properly notified, have participated and made contributions which might have produced a different administrative decision.
Reversed and remanded.