The Mareb River, also known as the Gash River, is a river flowing out of central Eritrea. Its chief importance is defining part of the boundary between Eritrea and Ethiopia, between the point where the Mai Ambassa enters the river at 14°53.6′N 37°54.8′E / 14.8933°N 37.9133°E to the confluence of the Balasa with the Mareb at 14°38′N 39°1.3′E / 14.633…The Mareb River, also known as the Gash River, is a river flowing out of central Eritrea. Its chief importance is defining part of the boundary between Eritrea and Ethiopia, between the point where the Mai Ambassa enters the river at 14°53.6′N 37°54.8′E / 14.8933°N 37.9133°E to the confluence of the Balasa with the Mareb at 14°38′N 39°1.3′E / 14.633°N 39.0217°E.