The landform produced when a river deposits its load at the point where it enters a lake or sea, forming a triangular-shaped plain, is known as a

A delta is a depositional landform that develops at the mouth of a river where it enters a standing body of water such as a sea or lake. The sudden reduction in velocity causes the river to deposit its sediment load, building up a triangular or fan-shaped plain. The Niger Delta in Nigeria is a classic example.