Lake Berryessa is the largest lake in Napa County, California. This reservoir in the Vaca Mountains is formed by the Monticello Dam, which provides water and hydroelectricity to the North Bay region of the San Francisco Bay Area.The lake is over 20,000 acres (80 km²) when full. It is approximately 15.5 miles (25 km) long but only 3 miles (5 km) wide. It has approximately 165 miles (265 km) of shoreline.
Near the dam on the southeast side of the reservoir is an open bell-mouth spillway, 72 feet (22 m) in diameter, which is known as the Glory Hole.
