What is the name of the body of water that a river flows into at its end?

The body of water that a river flows into at its end is referred to as an estuary. An estuary is an area where freshwater from a river meets and mixes with saltwater from the ocean. This region is characterized by its unique ecosystem, which is often rich in biodiversity and serves as crucial habitats for various species. Estuaries are generally found at the tidal mouth of a river, where the river's flow slows and sediment can accumulate, contributing to the formation of wetlands and other important environments.

While deltas, seas, and oceans are related bodies of water, they function differently. A delta is a landform created at the mouth of the river where sediment carried by the river water is deposited, typically creating new land as it spreads out into the adjacent body of water. Seas are generally larger bodies of saltwater partially enclosed by land, while oceans are the vast bodies of saltwater that cover most of the Earth's surface. The specific term "estuary" highlights the mixing of freshwater and saltwater, which is essential in defining this transitional zone where the river meets the sea.