What is the term for the wide part of a river where it nearly meets the sea?

The term for the wide part of a river where it nearly meets the sea is "an estuary." Estuaries are unique ecosystems that occur at the interface between river environments and maritime environments. They are characterized by the mixing of freshwater from rivers with saltwater from the ocean, creating a brackish water environment. This mixing results in high biological productivity and diverse habitats, making estuaries crucial for many species of fish, birds, and other wildlife.

Estuaries often serve as important nurseries for marine life, providing safe environments for juvenile fish and other organisms to grow and develop before they move into the open ocean. Furthermore, they act as filters for pollutants and sediments, helping to maintain water quality both upstream and downstream.

On the other hand, a lagoon typically refers to a shallow body of water separated from a larger body of water by a barrier such as a reef, while a delta is the landform created at the mouth of a river where it deposits sediment as it enters a standing body of water. A tributary is a smaller stream or river that flows into a larger one. Each of these terms describes different geographical features and processes, but they do not encapsulate the specific ecological and geographical characteristics of an estuary.