The 1960s were years of further unprecedented economic growth in the Tennessee Valley. Electric rates were among the nation's lowest and stayed low as TVA brought larger, more efficient generating units into service. Expecting the Valley's electric power needs to continue to grow, TVA began building nuclear reactors as a new source of cheap power. During this decade (and the 1970s), TVA was engaged in what was up to that time its most controversial project – the Tellico Dam Project. The project was initially conceived in the 1940s but not completed until 1979.