What is an estuary?

An estuary is specifically defined as a semi-enclosed coastal body of water where freshwater from rivers and streams meets and mixes with saltwater from the ocean. This unique environment is characterized by tidal fluctuations and is often rich in nutrients, making it a highly productive ecosystem. Estuaries serve as vital habitats for a diverse range of wildlife, including fish, birds, and other species, which rely on these areas for breeding, feeding, and shelter. They also play an essential role in filtering pollutants and stabilizing coastlines.

The other options do not accurately describe an estuary. A dense forest area may refer to a completely terrestrial ecosystem, devoid of the water dynamics present in an estuary. A swampy region of high altitude typically indicates a wetland environment that is distinct from the coastal interaction of estuaries. Similarly, a type of freshwater lake does not capture the brackish water mixing that is a hallmark of estuaries. Thus, the definition of a semi-enclosed coastal body of water connected to the open sea encompasses the essential characteristics of an estuary.