The Ubangi , a tributary of the Congo , also serves as part of the border between the CAR and the DRC .
The Mbomou merges with the Uele River to form the Ubangi River .
The Ubangi River , a tributary of the Congo , also serves as part of the border between the CAR and the DRC .
The Mbomou merges with the Uele River to form the Ubangi River .