Big Falls (also called Great Falls or Roar of Steam[1]) is a major waterfall located on the Missouri River in western Montana in the United States.

Although the falls used to flow powerfully year-round, most of the water is now diverted to the 60 megawatt hydroelectric plant of upstream Ryan Dam, reducing it to a trickle in the summer months.

[2] The dam raised the total height of the water to 177 feet.

[3] The Mandan Indians knew of the group of the falls and called them by a descriptive (but not formal) name: Minni-Soze-Tanka-Kun-Ya,[4] or "the great falls.

[7] Cottonwoods grow nearby, and the nearby shrubland habitat provides an environment for juniper, mule deer, and eagles.