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

A baymouth bar is a natural formation of sand or sediment that stretches across the mouth of a bay, effectively sealing it off from the open sea or lake. This accumulation of material is typically created by the action of longshore drift, where waves and currents move sand along the coastline.

Over time, this process can build up enough sediment to extend across the bay’s entrance, forming a barrier. Baymouth bars can lead to the creation of lagoons behind them as they prevent the free exchange of water between the bay and the larger 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.