The answer to the crossword is 'Niger', which is the third-longest river in Africa. The Niger River is a major river in West Africa, extending about 4, 180 km (2, 600 mi) in length and passing through Guinea, Mali, Niger, Benin, and Nigeria. It is the third-longest river in Africa, after the Nile and the Congo. The Niger is the principal source of water for much of West Africa and provides irrigation and hydroelectric power.