Black and white lantern Slide of Zambesi river - British South Africa. Part of Box 288, British South Africa. Boswell Collection. Slide number 17 Zambesi River - The Zambezi (also spelled Zambeze and Zambesi) is the fourth-longest river in Africa, and the largest flowing into the Indian Ocean from Africa. The 3,540-kilometre-long river (2,200 mi) has its source in Zambia and flows through eastern Angola, along the eastern border of Namibia and the northern border of Botswana, then along the border between Zambia and Zimbabwe to Mozambique, where it crosses that country to empty into the Indian Ocean.