Great Falls, Waterfall system on Missouri River, Montana, United States

Great Falls is a chain of five waterfalls on a 10-mile stretch of the upper Missouri River in north-central Montana: Black Eagle Falls, Colter Falls, Rainbow Falls, Crooked Falls and Big Falls, the last dropping 87 feet. The river descends 612 feet from the first fall to the last, over ledges of the Kootenai Formation, where softer sandstone erodes and harder rock forms the steps.

The Lewis and Clark expedition reached the waterfalls in June 1805 and took nearly a month to portage their equipment around them. Later dams altered the natural flow of water at several points along the falls.

The name recalls the moment when the Lewis and Clark expedition discovered the multiple cascades and recorded their size. Today, anglers use the waters below the falls, where trout gather in the calmer stretches of the river.

A viewpoint in Ryan Island Park offers a look at part of the falls and is accessible via a suspension bridge. The best months to visit are spring and early summer, when water levels are higher and the cascades appear fuller.

The amount of water flowing over the falls changes by season due to dam control upstream. In spring, the cascades can become nearly 900 feet wide, while in summer they shrink to several narrower streams.