The Okavango Delta (or Okavango Swamp), in Botswana, is the world's largest inland delta. The delta is very flat, with less than 2 meters variation in height across its 15,000 km². It is formed where the Okavango River flows into the vast Kalahari Desert. 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.
The Okavango Delta is both a permanent and seasonal home to a wide variety of wildlife which is now a popular tourist attraction. The Delta's average annual rainfall is 450mm, two thirds less than that of its Angolan catchment area, and most of it falls between December and March in the form of heavy afternoon thunderstorms.
Species include African Bush Elephant, African Buffalo, Hippopotamus, Lechwe, Topi, Blue Wildebeest, Giraffe, Nile crocodile, Lion, Cheetah, Leopard, Brown Hyena, Spotted Hyena, Greater Kudu, Sable Antelope, Black Rhinoceros, 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 and trees to graze, and then make their way back as winter approaches. Large herds of buffalo and elephant total about 30,000 beasts.