The Gilgel Abay (Amharic: ግልገል አባይ, Gǝlgäl Abbay), or Lesser Abay, is a river of central Ethiopia. Rising in the mountains of Gojjam, it flows northward to empty into south-western Lake Tana at 11.8°N 44°W. Tributaries of the Gilgel Abbay include the Ashar, Jamma, Kelti and the Koger. It was regarded as the true source of the Nile for a long time and the Jesuit priest Pedro Paez visited it in 1618. The name Gilgel Abbay means Lesser Nile, as Abbay is the name for the Blue Nile.
It is a meandering river, with a catchment area of 3887 km3. It is 71 meters wide near its mouth, with a slope gradient of 0.7 m/km. The average diameter of the bed material is 0.37 mm (sand).[1]
The river carries annually 22,185 tonnes of bedload and 7.6 million tonnes of suspended sediment to Lake Tana.[1]