the zambezi river and several tributaries of the congo river have their sources in angola. a large number of rivers originate in the central uplands, but their patterns of flow are diverse and their ultimate outlets varied. a number flow in a more or less westerly course to the atlantic ocean, providing water for irrigation in the dry coastal strip and the potential for hydroelectric power, only some of which had been realized by 1988. two of angola's most important rivers, the cuanza (kwanza) and the cunene (kunene), take a more indirect route to the atlantic, the cuanza flowing north and the cunene flowing south before turning west. the cuanza is the only river wholly within angola that is navigable—for nearly 200 kilometers from its mouth- -by boats of commercially or militarily significant size. the congo river, whose mouth and western end form a small portion of angola's northern border with zaire, is also navigable.