Kinshasa is a city of sharp contrasts, with affluent residential and commercial areas and three universities alongside sprawling slums. It is located along the south bank of the Congo River, downstream on the Pool Malebo and directly opposite the city of Brazzaville, capital of the Republic of the Congo. The Congo River is the second longest river in Africa after the Nile and has the continent's greatest discharge. As a waterway it provides a means of transport for much of the Congo Basin; it is navigable for river barges between Kinshasa and Kisangani; many of its tributaries are also navigable. The river is an important source of hydroelectric power, and downstream from Kinshasa it has the potential to generate power equivalent to the usage of roughly half of Africa's population.