The Great Blue Hole is a large underwater sinkhole off the coast of Belize. It lies near the center of Lighthouse Reef, a small atoll 62 miles from the mainland of Belize City. This large submarine vertical cave measures 984 feet in diameter and 407 feet deep. With its beautiful, clear water and the variety of wild marine life residing in its depths, the enormous blue hole is a popular scuba diving destination. Jacques Cousteau revealed the secrets of the mysterious Blue Hole to millions of viewers in 1971 through the television series The Undersea World of Jaques-Yves Cousteau. The Great Blue Hole is part of the larger Belize Barrier Reef Reserve System, a World Heritage site of the United Nations Educational, Scientific and Cultural Organization.