A shallow, often elongate coastal water body partially separated from the open ocean by a barrier such as a sand spit, barrier island, coral reef, or deltaic deposit. Lagoons exhibit restricted water exchange with the sea, resulting in variable salinity regimes ranging from brackish to hypersaline depending on tidal influx, evaporation rates, and freshwater input. They typically accumulate fine-grained sediments and support distinct ecological communities adapted to low-energy, sheltered conditions. Lagoon formation and stability are influenced by coastal geomorphology, sediment supply, sea-level fluctuations, hydrodynamic processes, and climatic factors. Subtypes include barrier-lagoon systems, reef lagoons, and choked, restricted, or leaky lagoons based on degree of oceanic connectivity.
