The White Nile flows sluggishly along with a low velocity and gentle slope; its course is generally straight and its section wide and shallow, banks low, supply very constant; the colour and limpidity of its water show very little change throughout the year, and the variations between the level of high and low supply are very small, being not more than 2 to 6 feet. The depth of the river in this stretch ranges from 15 feet at low Nile to 21 feet in flood. In parts, the channel in flood time is often of immense width. The result of 94 measurements made in June, 1862, show the mean width of the river in flood to be 1,870 yards. In many places, however, the channel is more than 2 miles wide, and in its general appearance it resembles a lake rather than a river. Its banks, more particularly the western shore, are very low, and its waters in flood spread for several miles over them. Their average height is not more than 8 to 10 feet above low water level, and the maximum difference between high and low supply is not more than 6 feet. The river is at its lowest by the beginning or middle of April; the rainfall in the south then causes a constant and gradual rise, but the flood does not reach its maximum before the beginning of September. The velocity of the current when in full flood is not more than 2½ to 3 miles an hour, whilst in winter this is reduced to 1½ miles an hour. The water is of an olive green or yellowish brown tinge. It owes most of its colour to the creamy-white waters of the Sobat River, called by the Arabs the Bahr El Asfar, or Yellow River. [Sidenote: Green water.] An odd phenomenon, the source of which has not been satisfactorily explained, is the “green water,” which makes its appearance at Dueim about the middle of May. The colour is owing to the mass of minute algæ in the water, which subsequently putrify and stink, but the origin of the water has not been definitely traced. It is believed to come from the upper Sobat, or Bahr El Ghazal, and not from the Bahr El Jebel. This green water reaches Cairo towards the end of June. [Sidenote: Junction of the Niles at Khartoum.] At Omdurman, half Nile usually occurs about the middle of July, high Nile at end of August or beginning of September, lasting about a month; half Nile end of November, lowest Nile end of April. The Blue Nile is at its lowest in May, and highest about the end of August. The result of careful measurements during the last 3 years has been to prove that when the Blue Nile is in flood, and generally when its discharge exceeds 5,000 metres cube per second, its waters hold back those of the White Nile and, owing to the increased depth in this river, due to the rise in the water levels, the volume coming from the south floods the Sudd marshes right and left of the channel and thus reduces the discharge of the White Nile by about 50 per cent. The average difference between low and high Nile here is 22 feet (17½ to 26 feet). [Sidenote: Below Khartoum.]