The Didessa (pronounced: ɗeɗ:e:s:a; Oromo: Dhedheessa) is a river in western Ethiopia. A tributary of the Abay River, it rises in the mountains of Gomma, flowing in a northwesterly direction to its confluence where the course of the Abay has curved to its southernmost point before turning northwards at about 9°57′N 35°41′E / 9.950°N 35.683°E. The Didessa's drainage area is about 19,630 square kilometers,[1] covering portions of the Benishangul-Gumuz Region and the West Welega Zone of the Oromia Region.
Tributaries on the right bank include the Enareya, Aet, Wama, and the Angar rivers; on the left side the most important tributary is the Dobana River. Exploring this river in the mid-1890s and from interviews with local inhabitants, Alexander Bulatovich asserted that downstream of its junction with the Angar, the Didessa is rapid-free and potentially navigable.[2]