San Diego Bay is a natural harbor and deepwater port located in San Diego County. San Diego Bay is considered one of the best natural harbors on the west coast, and spans 34 miles of waterfront. The bay, which is 12 miles long and 1 to 3 miles wide, is the third largest of the three large, protected natural bays on California’s entire 840 miles long coastline. In the northern part of the bay, there are two commercial “islands” called harbor Island and Shelter Island.