Lagoons
Lagoons are the shallow, protected bodies of water behind baymouth bars and barrier islands. These saltwater coastal lakes that are connected to the open sea by shallow, restricted outlets.
This is a picture of the Glenrock Lagoon in Australia. It is shallow because the water that could reach past the barrier islands or baymouth bars. Since there is a limited amount of water within the lagoon, water will slowly break down the area that sounds it in which it becomes wider.