The mouth of the San Francisco Bay is narrower than the bay itself.
Sounds and bays are indentations on the coastline along an ocean that take the form of naturally protected harbors. They are formed by glaciers, erosion, and sometimes by the hand of man. The terms are often used interchangeably and there are no regulatory rules on naming such places in English, other than convention. The habit of using the terms interchangeably, however, can be confusing to people trying to get a mental picture of the geographic feature under discussion. There are a few small differences between the two that can help distinguish a sound from a bay.
Fishing communities often base their fleets on sounds and bays as a means of providing protection for their ships.
A sound is an ocean inlet substantially larger than a bay and may be less protected. Sounds are often characterized by large open spaces of water. A sound may be deeper than a bay, and it is certainly deeper than a bay, a name for a shallow ocean inlet. It is also substantially wider than a fjord, an inlet formed along the coast by retreating glaciers.
On some maps, a channel or strait between two patches of land is identified as a sound; some settings require a sound to have at least two inputs. This is the case with Long Island Sound, the body of water that separates Long Island from neighboring Connecticut. It is also likely an example of the original use of the word “sound” in relation to geographic features, as the word derives from an Old English word meaning “to swim”, suggesting that a person could swim in a sound.
A bay, on the other hand, is a cove enclosed on three sides by terrain. The mouth of a bay can be narrower than the bay itself, as in San Francisco Bay, or it can be much wider, opening out into the open ocean. The Bay of Biscay, for example, has a very wide mouth, but is still recognizably surrounded by land on three sides. The bays also tend to be shallower than the sounds, and some of them need to be dredged to allow for ship traffic.
Both bodies of water are important geographic features, especially for sailors. Many fishing communities base their fleets on sounds and bays so their ships are safe, and sailors looking for anchor take advantage of the sheltered environment to rest from the open sea. Major port cities are almost universally located along the coast of a sound or a bay, to facilitate a large berthing area for the city’s commerce to thrive.