The boundary where fresh water feeds into salt water is called an estuary. Estuaries and the wetlands surrounding them are bodies of water that are commonly seen where rivers meet the sea. Estuaries are home to different animal groups and distinctive plants that have adapted to salty water, which is a combination of fresh water draining from the land and salty seawater. Estuaries are among the most productive ecosystems in the world. A lot of animals depend on estuaries for migration stopovers, places to breed, and food.