What is "baymouth bar"

A baymouth bar is a depositional feature as a result of longshore drift. It is a spit that completely closes access to a bay, thus sealing it off from the main body of water.

These bars usually consist of accumulated gravel and sand carried by the current of longshore drift and deposited at a less turbulent part of the current. Thus, they most commonly occur across artificial bay and river entrances due to the loss of kinetic energy in the current after wave refraction.