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.