Mont. Code Ann. § 85-1-223

The department may negotiate with the duly constituted authorities or agencies of other states and of the United States in the preparation of interstate compacts or agreements governing the use, distribution, and allocation of the water of any stream or streams flowing from Montana into such other states or flowing from such other states into Montana. It shall cooperate with other states and with the United States in making the necessary studies and obtaining the data necessary to the preparation of the compacts. This authority and the duties hereby imposed are limited to the preparation and proposal of the compact and the compact or agreement is not binding upon the state of Montana until approved by the legislature of Montana and the legislatures of the other state or states involved in the compact.