A depositional feature found at river mouths under certain conditions. Where the river enters the body of water (sea or lake) there is energy loss and load is deposited. If the rate of deposition exceeds the rate of removal in any current within the body of water then the material will build up. As the upper surface approaches sea-level the river may be forced to split into distributary channels which remain free of further deposition. Plants may colonize the top of the deposit and help it to build up above the sea level to form new land. Three types are identified: