Niger nī´jər [key], great river of W Africa, c.2,600 mi (4,180 km) long, rising on the Fouta Djallon plateau, SW Guinea, and flowing NE through Guinea and into Mali. In central Mali the Niger forms its vast inland delta (c.30,000 sq mi/77,700 sq km), a maze of channels and shallow lakes. An irrigation project in the delta, begun by the French in the 1930s and including a large dam at Sansanding (1941), has since opened some 250,000 acres (100,000 hectares) to farming, especially rice cultivation. Downstream from Timbuktu, Mali, the Niger begins a great bend, flowing first E and then SE out of Mali, through the Republic of Niger (where it forms part of the border with Benin), and into Nigeria the river also becomes increasingly polluted.

A hydroelectric and irrigation project, centered around the Kainji dam (1968), is located on the Niger near Jebba in E Nigeria. At Lokoja , central Nigeria, the Benue , its chief tributary, joins the Niger, which then flows south, emptying through a great delta into the Gulf of Guinea. The delta (c.14,000 sq mi/36,260 sq km)—the largest in Africa—is characterized by swamps, lagoons, and navigable channels. The region is a major source of palm oil and petroleum the exploitation of the latter has led to significant pollution of the water and land in some areas of the delta. Major towns in the delta are Port Harcourt and Bonny . Much of the Niger is seasonally navigable, and below Lokoja it is open to ships virtually all year. The Niger is a major source of fish, especially perch and tiger fish.

The upper Niger region was an important part of the former empires of Mali and Songhai . The course of the Niger long puzzled European geographers only from 1795 to 1797 did Mungo Park , the Scots explorer, correctly establish the eastern flow of the upper Niger, and it was not until 1830 that Richard and John Lander , English explorers, found that the river emptied into the Gulf of Guinea.

Benin, Burkina Faso, Cameroon, Chad, Côte dIvoire, Guinea, Mali, Niger, and Nigeria