The Jamma River is a river in central Ethiopia and a tributary of the Abay (or Blue Nile) on its right side. It drains parts of the Semien Shewa Zones of the Amhara and Oromia Regions. The Upper Jamma flows through steep, deep canyons cut first through volcanic rock and then through the Cretaceous sandstone and shaly sandstone, with Jurassic limestone at the bottom. It has a drainage area of about 15,782 square kilometers in size. Tributaries include the Wanchet.
The earliest mention of this river is in the Gadla of Tekle Haymanot, which was written in the fourteenth century. One of the earliest European mentions is by the missionary Pedro Páez, who was the first European to see and describe the origin of the Abay. According to Johann Ludwig Krapf, in the 1840s the Jamma defined the boundary between Marra Biete and Moret, two districts of the former province or kingdom of Shewa.