Deltas are deposits of sediments (particles of sand, gravel, and silt) at the mouths of rivers that flow into the ocean. The mouth of a river is the end where the body of water flows into the sea. Deltas are shaped by interactions of the river's fresh water with the ocean water, tides, and waves. Throughout history, deltas have been important places for human settlement. They are also vital habitats for many animals and plants. In the fifth century B.C.E, Greek naturalist Herodotus coined the name delta to describe the triangular shape of the sediments deposited at the end of the Nile River. The capital Greek letter delta (Δ) resembles a triangle. Most deltas are triangular in shape because rivers deposit larger amounts of sediment where they meet the sea, then fan out into the mouth of the sea to deposit the remaining sediment.

Formation of Deltas