Major dam construction started in Iran in the 1950s. Some fourteen large dams were built with the help of foreign engineers and advisors during two decades preceding the Islamic Revolution. In the post-revolution era, Iran's dam building capacity was significantly strengthened, with some 200 contracting companies, 70 consultant firms and 30 corporations as well as hundreds of hydroelectric manufacturing units having been established inside of Iran in less than three decades. In addition to the necessity of generating electricity, Iran needs dams to effectively control and manage a growing water shortage across the country.