Question: How long is the river that contains Colter Falls?

<P0-S0> Rainbow Falls (originally "Handsome Falls") is a waterfall on the Missouri River in Great Falls, Montana, just upstream from Crooked Falls and downstream from Colter Falls and Rainbow Dam. <P0-S1>  It is 47 feet (14m) high and 1,320 feet (402.3m) wide. <P0-S2>  The waterfall is part of the five Great Falls of the Missouri. <P0-S3>  The river spills over a sheer ledge of sandstone in the Kootenai Formation, forming the falls. <P0-S4>  The falls used to flow with a great deal of force year-round. <P0-S5>  In 1914 the river shortly upstream was dammed for hydroelectric power by the Rainbow Dam, which forms a run-of-the-river reservoir. <P0-S6>  As a result, the falls can almost totally dry up in the summer with only a few narrow strips of water trickling down its face. <P0-S7>  A railroad bridge crosses the river directly above the falls. <SEP> <P1-S0> Colter Falls, also Coulter Falls, (4.3m) waterfall, nearly 0.5 mi in width, part of the Great Falls of the Missouri, on the Missouri River in north-central Montana. <P1-S1>  Downstream of Colter Falls lies Rainbow Falls, and upstream is Black Eagle Falls. <P1-S2>  The Lewis and Clark Expedition was known to discover Westslope cutthroat trout at the base of the falls. <P1-S3>  The falls is now flooded in the impoundment behind Rainbow Dam. <P1-S4>  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. <P1-S5>  The falls was named by Paris Gibson, founder of the city of Great Falls, Montana, while they were not named by Lewis and Clark, who measured it at "6 feet 7 inches". <SEP> <P2-S0> Black Eagle Dam is a hydroelectric gravity weir dam located on the Missouri River in the city of Great Falls, Montana. <P2-S1>  The first dam on the site, built and opened in 1890, was a timber-and-rock crib dam. <P2-S2>  This structure was the first hydroelectric dam built in Montana and the first built on the Missouri River. <P2-S3>  The dam helped give the city of Great Falls the nickname "The Electric City." <P2-S4>  A second dam, built of concrete in 1926 and opened in 1927, replaced the first dam, which was not removed and lies submerged in the reservoir. <P2-S5>  Almost unchanged since 1926, the dam is 782 ft long and 34.5 ft high, and its powerhouse contains three turbines capable of generating seven megawatts (MW) of power each. <P2-S6>  The maximum power output of the dam is 18 MW. <P2-S7>  Montana Power Company built the second dam, PPL Corporation purchased it in 1997 and sold it to NorthWestern Corporation in 2014. <P2-S8>  The reservoir behind the dam has no official name, but was called the Long Pool for many years. <P2-S9>  The reservoir is about 2 mi long, and has a storage capacity of 1,710 acre.ft to 1,820 acre.ft of water. <SEP> <P3-S0> The Missouri River is the longest river in North America. <P3-S1>  Rising in the Rocky Mountains of western Montana, the Missouri flows east and south for 2341 mi before entering the Mississippi River north of St. Louis, Missouri. <P3-S2>  The river takes drainage from a sparsely populated, semi-arid watershed of more than half a million square miles (1,300,000 km), which includes parts of ten U.S. states and two Canadian provinces. <P3-S3>  When combined with the lower Mississippi River, it forms the world's fourth longest river system.