The Niger River is the main river of West Africa, extending about 4,180 kilometres. Its drainage basin is 2,117,700 km² in area. Its source is in the Guinea Highlands in south-eastern Guinea near the Sierra Leone border. It runs in a crescent shape through Mali, Niger, on the border with Benin and then through Nigeria, discharging through a massive delta, known as …The Niger River is the main river of West Africa, extending about 4,180 kilometres. Its drainage basin is 2,117,700 km² in area. Its source is in the Guinea Highlands in south-eastern Guinea near the Sierra Leone border. It runs in a crescent shape through Mali, Niger, on the border with Benin and then through Nigeria, discharging through a massive delta, known as the Niger Delta, into the Gulf of Guinea in the Atlantic Ocean. The Niger is the third-longest river in Africa, exceeded by the Nile and the Congo River. Its main tributary is the Benue River.