Ramayana mentions this river under the name of Kalimahi. The river is said to have been formed from the sweat of the cheeks of Vishnu when he performed austerities near its source.
Artemidoras speaks of a certain affluent of the Ganga as breeding crocodiles and dolphins. He named it Oidenes.
At the present time, Gandak is the only tributary of Ganga which breeds crocodiles. The Puranic tale of Gajehrajeha (fight between the elephant and crocodiles) is said to have taken place at its junction with the Ganga.
Therefore, Oidenes of Artemedoros is no other than the Gandak.