Ramganga (West) River originates from the western part of Dudhatoli reserve forest lying between Thailisain block in Pouri and Gairsain tehsil in Chamoli districts of Uttrakhand state. It is an important tributary of National River Gaga. The total length of the river is about 596 km. For first 200 km the river flows in Uttarakhand state and the remaining length falls in the state of Uttar Pradesh. Before it descends into plains, it is impounded by Kalagarh dam inside Jim Corbett National park.