Orographic lifting on the eastern and western sides of the Sudd contribute to that condition. Sudan had tried to increase water supplies by draining the Sudd wetlands of the south. The Sudd and the Okavango Delta are Africa's best known marshland areas. South Sudan includes the Sudd, one of the world's largest wetlands. The animal follows a nomadic annual migration cycle over the eastern Sudd floodplains. Dinka, Nuer and Shilluk pastoralists use the Sudd and the surrounding areas extensively. The Dinka remained in the Sudd area, maintaining their transhumance economy. The ancient Egyptians failed to penetrate the Sudd and reach the areas south of it. The Sudd provides food and water to large populations of migrating birds. The Sudd swamps which form the central part of the basin may still be subsiding. The Sudd flooded grasslands of southern Sudan divide this area into eastern and western blocks. Sudd was designated as a Ramsar Wetland of International Importance on 5 June 2006.