Lake Mead is the second-largest man made lake in the world, with over 150,000 acres of water (290 sq. mi.), two times bigger than the state of Rhode Island. When completely full it can hold over 28 million acre-feet of water, which is 9 trillion gallons, has a shoreline of 550 miles, and is 110 miles long and 274 square miles. Lake Mead's water is held in by the Hoover Dam.