Delta and Estuary both are made by the rivers at their mouth of sea, Delta is regarded as finest wildlife refuge and Estuaries are amongst the most heavily populated areas in the world. West flowing rivers of India does not form a Delta, they form Estuary, like Narmada and Tapti rivers.
A river delta occurs where a river enters an sea and the landform created by deposits of its material where the mouth of a river flows into an ocean. The Ganges Brahmaputra Delta is the largest river delta in the world at the Bay of Bengal.
An Estuary is a coastal water body of rivers with a connection to the open sea and formed a transition zone between river and ocean. Estuaries are the most natural productive habitats in the world and also amongst the most heavily populated areas.
Lagoon is a shallow coastal body of water separated from sea by a bar, islands or reefs. These Lagoons are fed by fresh river water or ocean tides and classified as coastal lagoons.