The Okavango River begins as the Cubango River in Angola and flows south, forming part of the border between Angola and Namibia. The 1,600 km-long Okavango river drains into the Moremi Wildlife Reserve in Botswana, forming a large (22,000 km2) fan-shaped inland delta within the Kalahari Desert. As the Okavango reaches its endpoint in the sands of the Kalahari Desert, the river breaks up into numerous channels, lagoons, and islands due to the shallow gradient. The rainy season upstream in Angola results in seasonal flooding in the Okavango delta, and water flow levels can vary significantly from year to year as well. Because freshwater sources are scarce in the Kalahari region, the swamps of the Okavango delta serves as a massive watering hole for a diversity of wildlife species. The beauty of this desert oasis and the concentration of African megafauna within the delta have made tourism an important part of the regional economy.