The longest river of Africa, and one of the most noted in the world's history; the Shimiyu, Isanga, and other streams which flow into Victoria Nyanza from the S. are regarded as its ultimate head-waters; from Victoria Nyanza, the Victoria Nile or Somerset River holds a north-westerly course to Albert Nyanza, whence it issues under the name of the Bahr-el-Jebel, swelled by the waters of the Semliki from Albert Edward Nyanza; about 650 m. N. it is joined by the Bahr-el-Ghazal from the W., and bending to the E., now under the name White Nile, receives on that side the Sobat, and as a sluggish navigable stream flows past Fashoda on to Khartoum, where it is met by the Bahr-al-Azrak or Blue Nile; 200 m. lower it receives the Atbara or Black Nile. Through Egypt the river's course is confined to a valley some 10 m. broad, which owes its great fertility to the alluvial deposits left by the river during it annual overflow (July to October, caused by seasonal rains in Abyssinia, etc.). From Khartoum to Assouan occur the cataracts; below this the stream is navigable. A few miles N. of Cairo begins the delta which lies within the Rosetta and Damietta—two main branches of the divided river—and is some 150 m. broad at its base. From Victoria Nyanza to the coast the river measures about 3400 m.