It is a meandering river. Near its mouth it is 950 meters wide. The bed material is sand.[3]
The river is about 965 kilometres (600 mi) long. In the wet season the flooded area covers 1,550 square kilometres (600 sq mi).
The headwaters of the river rise at elevations between 1,000 metres (3,300 ft) and 1,800 metres (5,900 ft) in the Angolan highlands. They drop steeply to the flat central Congo Basin at between 500 metres (1,600 ft) and 300 metres (980 ft) above sea level. A 2011 survey found 113 species of fish in 21 families and eight orders.[4]
^C.J. Warrington (May 1972). "M'Bwa na Basenji"(PDF). The Basenji. Retrieved 2012-02-02.
^Hanibal Lemma, and colleagues (2019). "Bedload transport measurements in the Gilgel Abay River, Lake Tana Basin, Ethiopia (Table 7)". Journal of Hydrology. 577: 123968. doi:10.1016/j.jhydrol.2019.123968. S2CID199099061.