San Diego Bay is a natural harbor and deepwater port located in San Diego County, California near the U.S.–Mexico border. The bay, which is 12 miles (19 km) long and 1 to 3 miles (1.6 to 4.8 km) wide, is the third largest of the three large, protected natural bays on California's entire 840 miles (1,350 km) long coastline after San Francisco Bay and Humboldt Bay.