The Okavango Delta (or Okavango Swamp), in Botswana, is the world's largest inland delta. It is formed where the Okavango River empties onto a swamp in an endorheic basin in the Kalahari Desert, where most of the water is lost to evaporation and transpiration instead of draining into the sea. Each year approximately 11 cubic kilometres of water irrigate the 15,000 km² area and some flood-waters drain into Lake Ngami. The Moremi Game Reserve, a National Park, spreads across the eastern side of the delta. The area was once part of Lake Makgadikgadi, an ancient lake that mostly dried up by the early Holocene.-------Chief’s Island, the largest island in the delta, was formed by a fault line which uplifted an area over 70 km long and 15 km wide. Historically it was reserved as an exclusive hunting area for the chief. It now provides the core area for much of the resident wildlife when the waters rise.---------Species include African Bush Elephant, African Buffalo, Hippopotamus, Lechwe, Topi, Blue Wildebeest, Giraffe, Nile crocodile, Lion, Cheetah, Leopard, Brown, Spotted Hyena, Greater Kudu, Sable Antelope, Black, White Rhinoceros, Plains Zebra, Warthog and Chacma Baboon. Notably the endangered African Wild Dog still survives within the Okavango Delta, exhibiting one of the richest pack densities in Africa. The delta also includes over 400 species of birds, including African Fish Eagle, Crested Crane, Lilac-breasted Roller, Hammerkop, Ostrich, and Sacred Ibis. The majority of the estimated 200.000 large mammals in and around the delta are not year round residents. They leave with the summer rains to find renewed fields of grass to graze on and trees to browse, then make their way back as winter approaches. Large herds of buffalo and elephant total about 30,000 beasts.The most populous large mammal is the lechwe antelope, with more than 60,000. A little larger than an impala with elongated hooves and a water repellent substance on their legs that enables rapid movement through knee deep water. They graze on aquatic plants and, like Waterbuck, take to water when threatened by predators. Only the males have horns.-------The Okavango Delta peoples consist of five ethnic groups, each with its own ethnic identity and language. They are Hambukushu (also known as Mbukushu, Bukushu, Bukusu, Mbukuschu, Ghuva, Haghuva), Dceriku (Dxeriku, Diriku, Gciriku, Gceriku, Giriku, Niriku), Wayeyi (Bayei, Bayeyi, Yei), Bugakhwe (Kxoe, Khwe, Kwengo, Barakwena, G/anda) and ||anikhwe (Gxanekwe, //tanekwe, River Bushmen, Swamp Bushmen, G//ani, //ani, Xanekwe). The Hambukushu, Dceriku, and Wayeyi are all Bantus who have traditionally engaged in mixed economies of millet/sorghum agriculture; fishing, hunting, and the collection of wild plant foods; and pastoralism. The Bugakhwe and ||anikwhe are Bushmen who have traditionally practised fishing, hunting, and the collection of wild plant foods; Bugakhwe utilized both forest and riverine resources while the ||anikhwe mostly focused on riverine resources. The Hambukushu, Dceriku, and Bugakhwe are present along the Okavango River in Angola and in the Caprivi Strip of Namibia, and there are small numbers of Hambukushu and Bugakhwe in Zambia as well. Within the Okavango Delta, over the past 150 years or so Hambukushu, Dceriku, and Bugakhwe have inhabited the Panhandle and the Magwegqana in the northeastern Delta. ||anikhwjjje have inhabited the Panhandle and the area along the Boro River through the Delta, as well as the area along the Boteti River. The Wayeyi have inhabited the area around Seronga as well as the southern Delta around Maun, and a few Wayeyi live in their putative ancestral home in the Caprivi Strip. Within the past 20 years many people from all over the Okavango have migrated to Maun, the late 1960s and early 1970s over 4,000 Hambukushu refugees from Angola were settled in the area around Etsha in the western Panhandle. The Okavango Delta has been under the political control of the Batawana (a Tswana sub-tribe) since the late 1700s. Most Batawana, however, have traditionally lived on the edges of the Delta. Small numbers of people from other ethnic groups such as Ovaherero and Ovambanderu now live in parts of the Okavango Delta, but since the majority of the members of those groups live elsewhere and the habitation is recent they are not considered as part of the Okavango Delta peoples. There are also several Bushmen groups represented by a handful of people. These groups were decimated by diseases of contact in the middle part of the 20th century, and most of the remaining members have intermarried with the ||anikwhe.