The ria and Estuary are both submerged coastal feature. An Estuary and a Ria are broad river mouths, which form narrow inlets in which sea water extends inland.

They are deeper and wider at the sea but narrower and shallower as it comes inland. The only difference is that a ria may be in a hilly coastal area.

In Africa the rias and estuaries cover 1000 km along the western coast stretching from Dakar in Senegal to Shabio Islands to the east of Sierra Leone and coast of Gambia.