The Sudd, a fast expanse of bogs and swamps, has inhibited the travel along the Nile for centuries. The Nile forms the Sudd because it enters a land of almost absolute flatness. The average slope from south to north along 400km of the Sudd is only 0.01%. The water has no real gradient to follow and no defined basin to pool into like in the Lakes of Albert, Edward, and Victoria. It is located in southern Sudan and hinders travel along the White Nile. Explorers dating back even to the Romans who were trying to find the source of the Nile found a hard and almost always insurmountable barrier in the Sudd. The Sudd is thick with reeds, grasses, water hyacinth, and other water loving plants. These can form massive blocks of vegetation that can shift position and block navigable channels creating an ever-changing network of water. Sometimes there is no channel a boat can travel on that will lead through the bog. Boats carry saws and chains to clear the floating islands of plants from the channel when the way through the area becomes lost.
In the rainy season the Sudd can expand to an area the size of all of England. In addition to the abundant plant life, there are a wide variety of animals that live in the marsh including many types of birds, fish, hippos, and of course mosquitoes which thrive in the warm, saturated air. The high water saturation in the air and fast expanse of marsh means that by the time the Nile exits the Sudd, it has slowed tremendously in speed and has lost a large amount of water to evaporation. There have been plans proposed in the past to create a channel for the Nile that bypasses the Sudd and allowing more water to make it to the river downstream in the deserts of northern Sudan and especially to Egypt. This would mean, however, the loss of habitat for the rich abundance of plant life in the area as well as the way of life for the tribes who live along and amongst the reeds and need the animals, plants, and water to survive. Civil war in Sudan, however, has stopped any and all building plans for water diversion from the Sudd.