Estuaries - Aquatic Ecosystems
All the rivers and lakes ultimately drain into the sea. However, many rivers develop a highly specialised zone before joining the proper sea. This zone is called estuary. An estuary is a transitional zone between rivers and sea representing an ecotone possessing unique ecological features and biotic communities.
Estuaries are the most productive ecosystems of the world. An estuary is semi-enclosed part of the coastal ocean containing brackish water that has free connection with the sea on one side and on the other side it is connected with a river mouth and receives fresh water.