It is called a River Delta.
The sediments are called silt or alluvium. The land formed from these sedimants where the river meets the ocean is a delta.
They are deposited at the river mouth, before it finally empties its water into the ocean.
The part of a river that empties into a body of water is called the mouth of the river
The Delta
The heaviest sediments like sand, small pebbles, and other detritus drop out of the current first. Lighter sediments like like silt are carried farther out.
Estuary
This is the river delta.
An estuary is an inlet of water where a river empties into an ocean or sea. It is formed from the freshwaters of rivers and stream, protected from storms, ocean waves and winds.
Euphrates River
It is usually referred to as the mouth of the river.
The Estuary Delta
a delta