Gandak: It originates in Tibet. Gandak joins Ganga in sonepur.
Ganga: Ganga has the highest catchment area in the state. Mahatma Gandhi Setu which is built on this river connects Patna and hajipur. It enters at chausa. Ghaghara, gandak, Bagmati, Kosi, and kali-Kosi is its northern tributary. Son, karmanasa, and punpun is its southern tributary.
Ghaghra: It is also known as Saryu. It originates in Nepal.
Kamla: Kamla barrage has been constructed on this river.
Phalgu
Kosi: Kosi is known as the sorrow of Bihar.
Mahananda: It originates in Sikkim. Mahananda joins Ganga at Nawabganj in Bangladesh.