The Blue Nile is a river originating at Lake Tana in Ethiopia. With the White Nile, the river is one of the two major tributaries of the Nile. The upper reaches of the river is called the Abbay in Ethiopia, where it is considered holy by many, and is believed to be the River Gihon mentioned as flowing out of the Garden of Eden in Genesis 2.
According to materials published by the Ethiopian Central Statistical Agency, the Blue Nile has a total length of 1,450 kilometres (900 mi), of which 800 km (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 kilometres (19 mi) of its source at Lake Tana, the river enters a canyon about 400 kilometres (250 mi) long. This gorge is a tremendous obstacle for travel and communication from the north half of Ethiopia to the southern half. The power of the Blue Nile may best be appreciated at Tis Issat Falls, which are 45 metres (148 ft) high, located about 40 kilometres (25 mi) downstream of Lake Tana.
There are numerous tributaries of the Abay between Lake Tana and the Sudanese border. Those on its left bank, in downstream order, include the Wanqa River, the Bashilo River, the Walaqa River, the Wanchet River, the Jamma River, the Muger River, the Guder River, the Agwel River, the Nedi River, the Didessa River and the Dabus River. Those on the right side, also in downstream order, include the Handassa, Tul, Abaya, Sade, Tammi, Cha, Shita, Suha, Muga, Gulla River, Temcha, Bachat, Katlan, Jiba, Chamoga, Weter and the Beles.