Mont. Code Ann. § 76-5-1102

Such cities, towns, or counties in accordance with the provisions of this part, individually, jointly, or severally or in cooperation with the federal or state government or any department or agency thereof and with each other, may deepen, widen, straighten, alter, change, divert, or otherwise improve the watercourses within or without their limits by constructing levees, dikes, embankments, structures, impounding reservoirs, or conduits and improve, widen, and establish streets, alleys, and boulevards across and adjacent to the abandoned or new channel or conduit and provide for the payment of the cost and maintenance of such project or projects under the terms of this part.