Mont. Code § 85-2-313
A permit issued prior to a final determination of existing water rights is provisional and is subject to that final determination. Upon petition, the amount of the appropriation granted in a provisional permit must be reduced, modified, or revoked by the department following a show cause hearing in which it is determined that reduction, modification, or revocation is necessary to protect and guarantee existing water rights determined in the final decree. Because a provisional permit is issued on a reasonable determination of legal availability under 85-2-311(1)(b), in a show cause hearing under this section, legal availability must be determined on a consideration of the final decree in the affected basin or subbasin. A person may not obtain any vested right to an appropriation obtained under a provisional permit by virtue of construction of diversion works, purchase of equipment to apply water, planting of crops, or other action where the permit would have been denied or modified if the final decree had been available to the department.
§ 85-2-313, MCA