Little is known of the state of the sudd during the years of the Mahdi and the Khalifa; but in 1898 Lord Kitchener found the Bahr el Gebel blocked by sudd immediately above Lake No; and about the same time Colonel Martyr, coming from Uganda, was unable to penetrate more than 20 miles north of Shambe for the same reason. As soon as the Khalifa had been finally crushed, operations to clear the channel were immediately undertaken. In the first three months a length of 80 miles of river had been cleared, including 5 miles of actual sudd in eleven blocks, besides three more blocks which broke away of themselves. The blocks that came away of themselves represented a very large amount of sudd. After one of them had burst, the floating weed took thirty-six hours to pass a given point. The effect produced by the sudd in damming up the river is illustrated by the fact that when the third block, which was nearly 20 feet thick, was removed, the upstream level fell 5 feet in four days, and all the swamps and lagoons began to drain into the river. The amount of labour was prodigious. At one place, owing to the enormous masses of um soof and papyrus that kept pressing into the river, no less than eleven clearances had to be made in one year. Five gunboats and 800 dervish prisoners, besides officers and guards, were employed. Sir W. Garstin gives an interesting description of the methods by which the sudd was removed: ‘In the first place, the papyrus and reeds on its surface were burnt (curious to relate, these green reeds burn readily when the marsh is dry), and in a few hours’ time the surface of the sudd was an expanse of blackened stalks and ashes. As soon as the fire had died down, gangs of men were landed from the steamer and employed in cutting trenches on the surface of the sudd. These trenches averaged from 0·60 to 0·80 metre in width, and from 1 to 1·25 metres in depth—_i.e._, as deep as the men could work. The surface was thus divided into a number of rectangular blocks some 3 metres by 4 metres. To these blocks were attached, one by one, steel hawsers and chains. This done, the steamer downstream went full speed astern. It invariably took several pulls to detach a block, and in some instances as many as nine were necessary. Both hawsers and chains kept constantly breaking, although the former were calculated to stand a strain of 35 tons per square inch, and the latter as much as 60 tons. As soon as a block was detached from the mass, it was allowed to float downstream. It was curious to see the green reeds and papyrus which had been confined beneath it reappear on the surface of the water. A horrible stench prevailed from the rotting vegetation.’