page_title: Missouri River
section_title: Dam-building era
hierarchical_section_title: Missouri River / Dam-building era
caption_attribution_description: English: Looking roughly south at en:Holter Dam in 1918, shortly after its completion. Holter Dam is located in Lews &amp; Clark County, Montana, United States. The dam powerhouse is on the right in the deep shadow. The metal structure holding the flashboards is visible at the crest of the dam. All the flashboards have been removed, allowing water to overflow the dam.
context_page_description: The Missouri River is the longest river in North America. Rising in the Rocky Mountains of western Montana, the Missouri flows east and south for 2,341 miles before entering the Mississippi River north of St. Louis, Missouri. The river drains a sparsely populated, semi-arid watershed of more than 500,000 square miles, which includes parts of ten U.S. states and two Canadian provinces. Although nominally considered a tributary of the Mississippi, the Missouri River above the confluence is much longer and carries a comparable volume of water. When combined with the lower Mississippi River, it forms the world's fourth longest river system.
  For over 12,000 years, people have depended on the Missouri River and its tributaries as a source of sustenance and transportation. More than ten major groups of Native Americans populated the watershed, most leading a nomadic lifestyle and dependent on enormous bison herds that roamed through the Great Plains. The first Europeans encountered the river in the late seventeenth century, and the region passed through Spanish and French hands before becoming part of the United States through the Louisiana Purchase.
context_section_description: In the late 19th and early 20th centuries, a great number of dams were built along the course of the Missouri, transforming 35 percent of the river into a chain of reservoirs. River development was stimulated by a variety of factors, first by growing demand for electricity in the rural northwestern parts of the basin, and by floods and droughts that plagued rapidly growing agricultural and urban areas along the lower Missouri River. Small, privately owned hydroelectric projects have existed since the 1890s, but the large flood-control and storage dams that characterize the middle reaches of the river today were not constructed until the 1950s.
  Between 1890 and 1940, five dams were built in the vicinity of Great Falls to generate power from the Great Falls of the Missouri, a chain of giant waterfalls formed by the river in its path through western Montana. Black Eagle Dam, built in 1891 on Black Eagle Falls, was the first dam of the Missouri. Replaced in 1926 with a more modern structure, the dam was little more than a small weir atop Black Eagle Falls, diverting part of the Missouri's flow into the Black Eagle power plant. The largest of the five dams, Ryan Dam, was built in 1913. The dam lies directly above the 87-foot (27 m) Big Falls, the largest waterfall of the Missouri.
  In the same period, several private establishments – most notably the Montana Power Company – began to develop the Missouri River above Great Falls and below Helena for power generation. A small run-of-the river structure completed in 1898 near the present site of Canyon Ferry Dam became the second dam built on the Missouri. This rock-filled timber crib dam generated seven and a half megawatts of electricity for Helena and the surrounding countryside. The nearby steel Hauser Dam was finished in 1907, but failed in 1908 because of structural deficiencies, causing catastrophic flooding all the way downstream past Craig. At Great Falls, a section of the Black Eagle Dam was dynamited to save nearby factories from inundation. Hauser was rebuilt in 1910 as a concrete gravity structure, and stands to this day.
  Holter Dam, about 45 miles (72 km) downstream of Helena, was the third hydroelectric dam built on this stretch of the Missouri River. When completed in 1918 by the Montana Power Company and the United Missouri River Power Company, its reservoir flooded the Gates of the Mountains, a limestone canyon which Meriwether Lewis described as "the most remarkable clifts that we have yet seen ... the tow[er]ing and projecting rocks in many places seem ready to tumble on us." In 1949, the U.S. Bureau of Reclamation (USBR) began construction on the modern Canyon Ferry Dam to provide flood control to the Great Falls area. By 1954, the rising waters of Canyon Ferry Lake submerged the old 1898 dam, whose powerhouse still stands underwater about 1 ¹⁄₂ miles (2.4 km) upstream of the present-day dam.
  "[The Missouri's temperament was] uncertain as the actions of a jury or the state of a woman's mind." 
  –Sioux City Register, March 28, 1868
  The Missouri basin suffered a series of catastrophic floods around the turn of the 20th century, most notably in 1844, 1881, and 1926–1927. In 1940, as part of the Great Depression-era New Deal, the U.S. Army Corps of Engineers (USACE) completed Fort Peck Dam in Montana. Construction of this massive public works project provided jobs for more than 50,000 laborers during the Depression and was a major step in providing flood control to the lower half of the Missouri River. However, Fort Peck only controls runoff from 11 percent of the Missouri River watershed, and had little effect on a severe snowmelt flood that struck the lower basin three years later. This event was particularly destructive as it submerged manufacturing plants in Omaha and Kansas City, greatly delaying shipments of military supplies in World War II.
  Flooding damages on the Mississippi–Missouri river system were one of the primary reasons for which Congress passed the Flood Control Act of 1944, opening the way for the USACE to develop the Missouri on a massive scale.
caption: Holter Dam, a run-of-the-river structure on the upper Missouri, shortly after completion in 1918
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