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From 1910 to 1913, construction was under way on a huge hydroelectric complex on the Mississippi River at Keokuk, Iowa. Located at the foot of the Des Moines Rapids, the project included a dam that was constructed from Keokuk to Hamilton, Illinois, on the eastern shore of the river. The power plant was separated from the western shore of the river by a navigation lock to permit barge and ship travel past the dam. Originally, all electric power generation at the site was at a frequency of 25 Hz, primarily due to the slow speed of the generators. The major portion of the station's output was transmitted to the city of St. Louis, Missouri, located about 140 miles to the south. As constructed, the station contained 15 10,000-hp turbines, each driving a 7.5-MW AC generator for a total station output of 112.5 MW. The Keokuk station is still in operation today, but it now generates 60-Hz power. The conversion from 25 Hz began in 1942, but was not completed until 2002.