The Okavango Delta (or Okavango Swamp), in Botswana, is a large inland delta, formed where the Okavango River reaches a tectonic trough in the central part of the endorheic basin of the Kalahari. All the water reaching the Delta is ultimately evaporated and transpired, and does not flow into any sea or ocean. Each year approximately 11 cubic kilometres of water spread over the 6,000-15,000 km² area. 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. Although the Okavango Delta is widely believed to be the World largest inland delta, it is, in fact not. In Africa alone there are two larger similar geological features - the Sudd on the Nile in South Sudan, and the Inner Niger Delta in Mali.
The Delta's profuse greenery is not the result of a tropical climate, rather it is an oasis in an arid country. The average annual rainfall is 450mm (approximately one third that of its Angolan catchment area) and most of it falls between December and March in the form of heavy afternoon thunderstorms.
December to February are hot wet months with daytime temperatures as high as 40°C, warm nights, and humidity levels fluctuating between 50 and 80%. From March to May the temperature becomes far more comfortable with a maximum of 30°C during the day and mild to cool nights. The rains quickly dry up leading into the dry, cold winter months of June to August. Daytime temperatures at this time of year are mild to warm but the temperature begins to fall after sunset. Nights can be surprisingly cold in the Delta with temperatures barely above freezing.
September to November sees the heat and atmospheric pressure build up once more as the dry season slides into the rainy season. October is the most challenging month for visitors - daytime temperatures often push past 40°C and the dryness is only occasionally broken by a sudden cloudburst.
The Okavango delta is both a permanent and seasonal home to a wide variety of wildlife which is now a popular tourist attraction. Species include African Bush Elephant, African Buffalo, Hippopotamus, Lechwe, Tsessebe, Sitatunga, Blue Wildebeest, Giraffe, Nile crocodile, Lion, Cheetah, Leopard, Brown Hyena, Spotted Hyena, springbok, 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, Pel's Fishing Owl, 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.