Or. Admin. R. 690-030-0075
Any number of persons, firms, or corporations, jointly interested in the subjects enumerated in the notice of contest may appear as parties contestant therein; and any number of persons, corporations, or associations claiming interest adversely to the rights claimed by said contestants, and who shall have submitted proof of their claim to the Water Resources Director, may be jointed as parties contestee, in the statement of contest.
ORS 536 & 543
WRD 3, f. & ef. 2-18-77