Usually it would be an estuary.
A river mouth is a portion of a stream where it merges with another stream. Note that here the definition of stream is not "a small river", but "any flowing current within well defined banks."
The mouth of a river where it meets the sea, with a mixing of fresh and salt tidal water
a nearly flat plain of alluvial deposit between diverging branches of the mouth of a river
In geographical terms, the word mouth means an opening into a place such as a cave or volcano. It also means a place where a stream meets with another stream, such as the mouth of a river.
Delta - Mouth of a river Alluvium - Fertile sediment deposited by a river Meaner - Curve in a river Tributary - Stream that flows into a river -Apex- :)
an example of a river mouth would be the mouth of the Mississippi river
The mouth of the river is at the end of the riveri
The mouth of the river is at the end of the riveri
The mouth of a river is the open space at the end of a river allowing passage. The mouth of a river, sometimes called a delta, is the point at which the river ends and the water flows into the sea.
"The canoe entered through the mouth of the river." "The mouth of the river was a good place for fishing." :)
the mouth of a river is the begining of a river
Many words have no apparent antonym. If an estuary is the mouth of a river, 'source' might be one, by some definition.