Sudd (sŏd) [key], swampy region, c.200 mi (320 km) long, and c.150 mi (240 km) wide, central South Sudan, E central Africa. It is fed by the Bahr el Jebel, the Bahr el Ghazal, and the Bahr el Arab, headwaters of the Nile. Thick aquatic vegetation (sudd) disperses the river water into numerous channels. About half the water is lost through evaporation and absorption before leaving the Sudd.
The vegetation hinders navigation and long barred attempts to trace the Nile to its source. An Egyptian expedition first succeeded in crossing the Sudd in 1840. It took much effort to clear (1899–1903) a channel for regular navigation, and constant maintenance is necessary to keep it open. Construction on a canal to circumvent the Sudd and drain swampland for agriculture began in 1978 but was suspended in 1983.