What is an estuary?

An estuary is specifically defined as a coastal body of water where freshwater from rivers and streams meets and mixes with saltwater from the sea. This mixing creates a unique environment that is often rich in nutrients, supporting diverse ecosystems. Estuaries serve as critical habitats for a variety of wildlife, including birds, fish, and other organisms, many of which rely on these areas for breeding, feeding, and shelter.

In contrast to the other choices, an estuary is not primarily characterized by erosion, nor is it representative of a type of freshwater lake or a completely enclosed body of water. Instead, its defining feature is the interaction between freshwater and saltwater, which fosters a distinct ecological zone vital to both aquatic and terrestrial life.