Formation
Rivers move slowly at the river mouth. The river carries a lot of sediment and mud. The river deposits (drops) its sediment and mud at its mouth. This sediment and mud spreads out into a fan- like shape, or delta, across the mouth of the river.

If the force of the sea tides and water is not very strong, the mud deposits cannot be washed away. Instead, the deposits break up the flow of the river water into many smaller channels. The delta gradually gets bigger and bigger. The new land is made up of billions of pieces of mud, sediment and small rocks. This sediment has been carried by the river from its source to its mouth.

A delta is often triangular in shape. It gets its name from the Greek letter 'delta' which is shaped like a triangle. Not all deltas look the same, but they all split the river into many different channels. The channels in a delta are called distributaries.

A satellite photo of the Ganges Delta in India

Facts

• The world's best known delta is the Nile delta in Egypt.

• The largest delta in the World is found partly in India and partly in Bangladesh. It is formed by two rivers, the Ganges and the Brahmaputra. The Ganges delta covers an area the size of Scotland.

• Some deltas are getting smaller. The Nile delta is getting smaller because sediment cannot get through the Aswan High Dam.

• Ships can sail through the large deltas such as the Mississippi or the Nile. 

• The Selina Channel (canal) is one of three channels built on the Rhine delta to let ships pass through.

• Deltas have very fertile soil and are a good place to grow crops on.

• A lot of wildlife lives in deltas. The Camargue is the delta of the river Rhone and is a haven for plant, animal and bird species.

• Some people live in river deltas. The Warao people live in the Orinoco delta and the Lipovani people live in the Rhine delta.

Deltas and ships
Many deltas are wide enough for ships can use them to carry cargo from inland to the sea. Ships may also travel up deltas inland to deliver cargo and goods. But the channels of the delta can become blocked with a lot of sand, silt and mud. Sand bars form, making the channels shallower. Ships can get stuck on these sand bars, which is dangerous. Often delta channels have to be cleared by machines known as dredges. The dredge is like a giant vacuum cleaner. It picks up all the sand, silt and mud from the river bottom and deposits it back on the river banks again.

A dredging ship

The Mississippi Delta