Which river is the right tributary of the Nile?
The Blue Nile is a river originating at Lake Tana in Ethiopia. With the White Nile, it is one of the two major tributaries of the Nile. The Blue Nile supplies about 80% of the water in the Nile during the rainy season. The Blue Nile is so called because floods during the summer monsoon erode a vast amount of fertile soil from the Ethiopian Highlands and carry it downstream as silt, turning the water dark brown or almost black.
According to materials published by the Central Statistical Agency, the Blue Nile has a total length of 1,450 kilometres (900 mi), of which 800 kilometres (500 mi) are inside Ethiopia. The Blue Nile flows generally south from Lake Tana and then west across Ethiopia and northwest into Sudan. Within 30 km (19 mi) of its source at Lake Tana, the river enters a canyon about 400 km (250 mi) long. This gorge is a tremendous obstacle for travel and communication from the north half of Ethiopia to the southern half. The canyon was first referred to as the "Grand Canyon" by the British team that accomplished the first descent of the river from Lake Tana to near the end of the canyon in 1968.