A delta is a landform that forms at the mouth of a river where it meets a body of water, typically an ocean or a lake. Deltas are characterized by the deposition of sediment carried by the river as its flow slows down upon entering standing water. This accumulation of sediment creates fertile land that supports diverse ecosystems and is often ideal for agriculture. Famous examples of deltas include the Mississippi River Delta in the United States and the Nile Delta in Egypt.