The term 'River Mouth Area' refers to the area where a river meets the sea. This area is typically characterized by two distinct features: an ESTUARY and a DELTA. An ESTUARY is a partially enclosed coastal body of water where fresh water from rivers and streams mixes with salt water from the ocean. A DELTA is a landform created by sediment deposits at the mouth of a river, often forming a triangular shape. Both estuaries and deltas are important ecosystems that provide habitats for many species of plants and animals.