Estuary

An estuary is a partially enclosed coastal body of brackish water where freshwater from rivers or streams meets and mixes with saltwater from the open sea. It sits as an ecotone, a transition zone shaped by both marine forces such as tides, waves and salt intrusion and fluvial forces such as freshwater flow and sediment transport, and the resulting mix of nutrients makes estuaries among the most productive natural habitats on Earth. Most of today's estuaries are geologically young, having formed within roughly the last ten to twelve thousand years as Holocene sea level rise flooded valleys that rivers had cut or that glaciers had scoured. Estuaries are classified by salinity distribution, geomorphology, water circulation and energetics, and related features that go by other names, such as certain bays, harbors, lagoons, inlets or sounds, do not always meet the strict technical definition of an estuary.