Colter Falls, also Coulter Falls, (4.3m) waterfall, nearly 0.5 miles (0.80 km) in width, part of the Great Falls of the Missouri, on the Missouri River in north-central Montana. Downstream of Colter Falls lies Rainbow Falls, and upstream is Black Eagle Falls. The Lewis and Clark Expedition was known to discover Westslope cutthroat trout at the base of the falls. The falls is now flooded in the impoundment behind Rainbow Dam. As Rainbow Dam's reservoir is a run-of-the-river reservoir, it rarely is emptied, so the falls is rarely seen even in extreme drought.