Muscle Shoals, town (1990 pop. 9,611), Colbert co., NW Ala., on the Tennessee River opposite Florence; inc. 1923. Chemicals, truck trailers, and nuts, screws, and bolts are manufactured. The river formerly descended in a series of unnavigable rapids called Muscle Shoals (c.35 mi/56 km long with a drop of more than 130 ft/40 m). The river became the site of a canal built by the state in the 1830s, but later it silted up and was abandoned; in 1890 a successful canal was constructed by U.S. army engineers. The area was bought (1933) by the Tennessee Valley Authority (TVA), which planned to develop hydroelectric power and navigation. The building of Wilson Dam (1925) and of Wheeler Dam (1936) resulted in the submersion of the Muscle Shoals rapids by about 10 ft (3 m) of water. The TVA's Environmental Research Center, the Public Power Institute, and the International Fertilizer Development Center are in Muscle Shoals.