Ameren Corporation is an American power company created December 31, 1997, by the merger of St. Louis, Missouri's Union Electric Company and the neighboring Central Illinois Public Service Company of Springfield, Illinois. It is now a holding company for several power companies and energy companies. The company is based in St. Louis, with 2.4 million electric, and 900,000 natural gas customers across 64,000 square miles in central and eastern Missouri and the southern four-fifths of Illinois by area. Ameren is the holding company for the following: Ameren Missouri Ameren Illinois Ameren Transmission Company Ameren Services The Ameren Missouri subsidiary owns Bagnell Dam on the Osage River, which forms the Lake of the Ozarks. Ameren Missouri is responsible for managing water levels on the lake according to federal regulations. Wikipedia