Mixed-fed rivers are fed by tributaries of more than one of the above classes and show no clear dominance of one of the above classes. 

The Kamla is a foothills-fed system, whereas the Balan is a plains-fed system. After some 150 to 200 km of independent flow, they join and flow together for some 40 km before joining the Kosi. This has been classified as mixed-fed-system. The two existing hydrological stations are located on the tributary systems, Jaynagar on the Kamla and Jhanjharpur on the Balan.