Great Falls, Natural cascade system in central Montana, United States

Big Falls is the lowermost and largest of the Great Falls of the Missouri, dropping 87 feet (27 m) and up to 900 feet (270 m) wide at peak flow. It lies on the Missouri River in western Montana, and upstream Ryan Dam raises the total fall to 177 feet.

William Clark of the Lewis and Clark Expedition named the specific Grand Falls in 1805, not Meriwether Lewis. The Mandan people already knew the group of falls, calling them Minni-Soze-Tanka-Kun-Ya, "the great falls." The falls are the lowermost and largest of the Great Falls of the Missouri, 87 feet high and up to 900 feet wide at peak flow.

Native American tribes relied on the falls area for generations as important fishing grounds and established trading routes near these waters. The waterfalls were central to the lives and commerce of peoples living in the region.

Ryan Island Park provides the main viewing area with a suspension bridge crossing the Missouri River for close views of the waterfalls. Be prepared for water levels that vary significantly with seasons and weather conditions.

The falls once ran powerfully all year, but most of the Missouri's water is now diverted to the 60-megawatt Ryan Dam plant upstream, leaving only a trickle in summer. The dam also raised the total drop to 177 feet. The Mandan called the group Minni-Soze-Tanka-Kun-Ya, "the great falls."