In the Sudd, the river flows through multiple tangled channels in a pattern that changes each year. Papyrus grows in dense thickets in the shallow water, which is frequented by crocodiles and hippopotamus. Sometimes the matted vegetation will build up into an island, but these eventually break up.
There are three main waterways through the swamp; the Bahr-el-Zaraf ("River of the Giraffes"), the Bahr-el-Ghazal ("River of the Gazelles"), and the Bahr-el-Jebel, which is the main connection to the Mountain Nile. The early explorers searching for the source of the Nile experienced considerable difficulties, sometimes taking months to get through.
In The White Nile, Alan Moorehead says of the Sudd, "there is no more formidable swamp in the world".