The widened river mouth found at the point where a river enters the sea.

An estuary is a partially enclosed coastal body where freshwater from rivers meets and mixes with saltwater from the ocean. The widened mouth occurs due to the deposition of sediments as the river's current slows upon entering the sea. Eskers are glacial ridges, peninsulas are land extensions, hamadas are desert plateaus, and aquifers are groundwater reservoirs.