What is the name of the broad seaward end of the river mouth?

Answer 1

The broadened seaward end or extension of a river is known as the delta. It is in this area that the river will deposit excess mud on its way to the sea. Much of the delta is often very marshy and divided into many small waterways.

Answer 2

The broadened seaward end or extension of river is called a river delta. It is a triangular tract of sediment that has been deposited at the mouth of a river.