Lake Berryessa is the largest lake in Napa County, California. This reservoir is formed by the Monticello Dam, which provides water and hydroelectricity to the North Bay region of the San Francisco Bay Area. he lake was named for the first European settlers in the Berryessa Valley, José Jesús and Sexto "Sisto" Berrelleza (a Basque surname, Anglicized to Berreyesa then later respelled Berryessa), who were granted Rancho Las Putas in 1843.
The lake has been heavily used for recreational purposes and encompases over 20,000 acres (80 km²) when full. The reservoir is approximately 15.5 miles (25 km) long, but only 3 miles (5 km) wide.
Open Water Swimming
The Lake Berryessa Open Water Swim is a 1-mile and 2-mile open water swim held annually in early June in Lake Berryessa that annually draws several hundreds of masters swimmers. The multi-race event is one of America's Top 100 Open Water Swims and was site of the 2014 U.S. Masters Swimming open water swimming championship.