The dam derives its name from Bagnell, Missouri at the dam site which preceded the dam. It in turn derives its name from William Bagnell, who platted the town in 1883. A variant name is the "Osage Dam".
Construction started on the dam in 1929 and was completed in 1931. The resulting reservoir, the Lake of the Ozarks, has a surface area of, over of shoreline, and stretches from end to end. At the time of construction, it was one of the largest man-made lakes in the world and the largest in the United States. Its construction virtually ended commercial traffic on the upper river. The concept of a hydro-electric power plant on the Osage River was first introduced by a Kansas City developer as early as 1912. Ralph Street managed to put together the funding to construct a dam across the Osage River. He began building roads, railroads, and the support structures necessary to begin construction of a dam that would impound a much smaller lake than what is now known as Lake of the Ozarks. Sometime in the mid-1920s, Street's funding dried up, and he had to abandon the idea of the first hydroelectric power plant on the Osage River. Union Electric Power and Light stepped in with engineering firm Stone & Webster from Boston, Massachusetts. It designed and constructed Bagnell Dam in one of the most unlikely spots along the Osage River. Many thought the $30 million project would be a disaster after the stock market crash of 1929, but it was completed. Employment during the lengthy construction proved to be a boost to many families in the area, as well as the hundreds of workers attracted from other areas of the country. By early 21st-century standards, all construction was done by hand, and the equipment used in the construction was quite primitive. The construction of Bagnell Dam was completed and Lake of the Ozarks was a full reservoir in fewer than two years. The stock market crash of 1929, which precipitated the Great Depression, occurred just months after construction began on Bagnell Dam. The project employed thousands of laborers, providing a large economic boost to the rural area around the dam and to the state as a whole at a time when jobs were scarce. The associated Union Electric Administration Building-Lakeside was constructed in 1930. This building was added to the National Register of Historic Places in 1998, with a boundary increase of associated property in 2011.
Floodgates
Construction of the dam allowed for thirteen floodgates, as called for in the original design. Only twelve floodgates were installed, and the thirteenth spillway opening is walled shut with concrete. The engineers calculated that twelve floodgates provided a large enough margin of safety.
The Bagnell Dam and the Lake of the Ozarks reservoir feature prominently in the Netflix television series Ozark. The reservoir's displacement of the fictional Snell family left a legacy of distrust and antipathy to outsiders and developers. For the Snells, this distrust feeds a lust for just retribution and influences how they view the politics of development around the lake and why they get involved in an effort to bring a casino.
