Mont. Code Ann. § 85-8-801

All drain districts of the state of Montana organized prior to March 1, 1921, and continued in existence pursuant to section 100, Chapter 129, Laws of 1921, shall continue their existence as drain districts under and pursuant to all of the provisions of drainage district laws, and the commissioners of such drain districts shall have all the power and authority conferred by the drainage district laws upon the commissioners of drainage districts.