Construction of the original Don Pedro Dam was finished in 1923. It was the tallest dam in the world. However, since it could not meet the irrigation needs after several dry winters, the City and County of San Francisco joined with two irrigation districts to construct a much larger dam that was begun in 1967 and completed four years later at the cost of $105 million. At the time known as the New Don Pedro Project, it is now known as the Don Pedro Reservoir, Lake Don Pedro, or Don Pedro Lake. Built mainly to store irrigation water, the reservoir has additional benefits that include flood control, power generation, and recreation. The old dam is still 250 feet below the surface of the reservoir.