At its delta at the Mediterranean Sea, the Nile broadens into a large fan-shaped alluvial plain. Credit: NASA.
A delta is a flat alluvial plain (see alluvium) at a river mouth or at the confluence of two rivers, formed of fertile mud deposited by the slowing-moving water. Typically, the stream divides and subdivides until a fan-shaped plain (see alluvial fan) covered by a complex of channels results. The form of a delta depends of the rates of sedimentation and of erosion by the sea.