River delta

A delta is a  landform where the mouth of a river  flows into an ocean, sea, desert, estuary, lake or another river. It builds up sediment outwards into the flat area which the river's flow encounters (as a deltaic deposit) transported by the water and set down as the currents slow. Deltaic deposits of larger, heavily-laden rivers are characterized by the main channel dividing amongst often substantial land masses into multiple streams known as distributaries. These divide and come together again to form a maze of active and inactive channels.
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