River delta

landform that is formed at the mouth of a river

A river delta is a landform where the mouth of a river flows into an ocean, sea, desert, estuary, lake or another river. It is formed by sediment carried by the river being deposited in the wider mouth. This happens because the water moves less quickly there.

Nile River delta, as seen from Earth orbit. Photo courtesy of NASA

The word "delta" comes from the upper-case letter delta, Δ , in the Greek alphabet because many river deltas are triangular like this letter.

A river delta can cover just a few square miles, or an area of hundreds or thousands of square miles of land.

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