The Okavango Inland Delta is an unique ecological wonder in the northern part of Botswana. Located in the Kalahari Desert, this unusual oasis of lush greenery is flooded once a year by summer (Jan-Feb) rainfall onto the upper reaches of the Okavango River in Angola. Upon reaching this very flat part of the Kalahari Desert, the water floods the entire basin, transforming the region (roughly rectangular region 250km by 150km) into a swampy delta of islands and water channels.
For the next four months, wildlife and flora flourish in the region, till eventually, much of the water is washed into the dry sands of the Kalahari, or is evaporated. Then, most of the delta dries up. The larger wildlife migrates out of the region to water sources elsewhere, while other wildlife, e.g., fish and crocodile, restrict themselves to the much reduced main channel of the Okavango River, or hibernate within wet mud.