The Ganges River (Ganga River) is 1,560 mi (2,510 km) in length, with its source high in the Himalayas. The river carries a very high sediment load and has unstable banks that frequently migrate. The Ganges Basin, which includes parts of India, Nepal, China, and Bangladesh, has one of the highest human population densities in the world. The river generally flows eastward and in Bangladesh empties into the Bay of Bengal. Here the Brahmaputra River and the Ganges River combine to form the largest delta in the world, which contains large population centers, fertile agricultural land, and the vast Sunderbans mangrove forest. The delta is a complex network of mudflats, beach ridges (called cheniers), tidal channels, and mangrove islands. According to religious tradition, the Ganga River is a symbol of purification.