River delta The Okavango Delta in Botswana is one example. The generic term "mega delta" can be used to describe very large Asian river deltas, such as the Yangtze, Pearl, Red, Mekong, Irrawaddy, Ganges-Brahmaputra, and Indus. The formation of a delta is complicated, multiple, and cross-cutting over time, but in a simple delta three main types of bedding may be distinguished: the bottomset beds, foreset/frontset beds, and topset beds. This three part structure may be seen in small scale by crossbedding. The Ganges/Brahmaputra combination delta, which spans most of Bangladesh and empties into the Bay of Bengal, is the world's largest delta.
Indus River Delta (however, the delta has lost 170,000 hectares of mangroves over the past 50 years). The delta faces pollution both from sea and the Indus river. Chemical run-off into the river threatens many species. Most of this chemical run-off consists of agriculture pesticide and fertilizer. The delta faces pollution from the Arabian Sea. Karachi, Pakistan's largest city, releases sewage and discharge from industrial units into the Arabian sea, most of which is untreated. Both Port of Karachi and Port Qasim handle significant shipping traffic, resulting in oil discharge, some of which reaches the delta. All of this pollution lowers the river