‘Aţbarah (river), also called the Black Nile, the only tributary of the Nile River north of Khartoum, Sudan. It is 1,120 km (696 mi) long, and rises in the Ethiopian highlands west of Gonder, and not far from Lake T’ana. It flows northwest into Sudan, where it joins the larger Tekezee tributary. The ‘Aţbarah then joins the Nile at the town of ‘Aţbarah. From June to August the river is swollen by the summer rains, and provides more than one-fifth of the Nile’s total volume of water. It also brings down millions of tons of silt every year, which adds to the accumulations in Lake Nasser behind the Aswān High Dam. From November to May the ‘Aţbarah dwindles to a mere trickle, and appears only as a series of pools.