A lagoon is a water area surrounded by partially intercepted seawater between an offshore sandbank and the coast. The water in the lagoon is pure water at the beginning, and the seawater inside and outside can be circulated by the tidal mouth between the offshore Shazhou. Since the offshore sandbar isolates most of the waves, the tidal sediments are gradually deposited in the lagoon. The formation of Dapeng Bay is caused by the sedimentation of the sand mouth formed by the drift of the current monsoon from the upstream and downstream of the Donggang River and the Linbian River. The sand mouth topography is formed by the extension of the sand into the sea. A narrow ridge of gravel, which crosses the bay,exit and closes the bay, thus forming the Dapeng Bay lagoon terrain.
In the marginal zone of the sea, lagoons of different water properties can be formed due to incomplete isolation or periodic isolation of seawater, resulting in salinization or desalination of the aqueous medium. The barriers can be isolated, such as barrier islands, sand bars, beaches, sand dunes, and shoals.The coastal and tidal currents carry or carry a considerable amount of solid material (sand, pebbles) along the bottom, in some parts of the shore the flow strength is no longer sufficient to move this material, and it begins to settle to the bottom, where the underwater elongated shafts bars). Gradually increasing, the bar comes to the surface of the sea – at first only at low tide, and then it completely cuts off the water strip from the sea. So a lagoon bank is formed – in it, behind the sandy (gravel, pebbly or shell) strip of the shore bar is a narrow, stretched along the coast to tens and even hundreds of kilometers of the lagoon. In the junctions of the two opposing streams of sediments, triangular lagoons can form.
As the isolation of the water in the lagoon begins to differ from the sea. Specific lagoon precipitates are formed, composed of very small particles, often precipitation of salts from water. Coral lagoons can be stretched along the shore if separated from the sea by barrier coral reefs. Constantly or during tides, coral lagoons communicate with the sea through numerous straits. The water inside the coral lagoons, as a rule, does not differ from the sea, as it is constantly updated. Coral lagoons are formed inside ring coral reefs (atolls). Their size varies from a few kilometers to tens of kilometers in diameter.
The coastal lagoon is located between the shore dam and the coast. The waters are narrow and irregular; the coastal lagoons can be divided into brackish water, salt water and salt water according to salinity. Brackish water lagoons receive more runoff.Extremely saltwater lagoons are formed where evaporation exceeds seawater influx.