Lagoons

A lagoon is a shallow, typically long and narrow body of water that is separated from a larger sea or ocean by a barrier such as a sandbar, barrier island, reef, or spit. Lagoons can be saline, brackish, or, in some cases, freshwater, with salinity largely determined by the balance between tidal exchange with the sea and freshwater inflows from rivers and rainfall. They occur along coastlines and in some inland settings where barriers isolate a portion of water from the main body of water.

Coastal lagoons form behind barrier formations that restrict direct sea access, while estuarine or riverine lagoons develop where rivers create depressions with limited connection to the open sea. Inlets and tides control exchange, water level, and salinity, but sedimentation over time can gradually fill lagoons, altering their depth and ecology. Lagoons are often dynamic systems, with shifts in barrier position, inlet openings, and hydrology affecting their size and character.

Ecology and human use: Lagoons typically harbor high biological productivity and serve as important nursery habitats for fish and crustaceans. They may contain seagrass beds, salt marshes, mangroves, and diverse bird life. Economically, lagoons support fishing, tourism, and sometimes shipping, but many face pressures from development, pollution, dredging, and changes in sediment supply. Climate change and sea-level rise can influence barrier integrity and salt balance, with cascading effects on salinity, sedimentation, and habitat viability.

Examples include the Venetian Lagoon in Italy and the Curonian Lagoon in the Baltic region, among numerous tropical and temperate coastal systems worldwide. Lagoons represent a key interface between marine and freshwater environments and a notable component of coastal wetlands.