The Tons River is the longest tributary of the Yamuna River. It flows through Garhwal, the western part of the Himalayan state of Uttaranchal. The river originates at an elevation of 3,900 m and joins the Yamuna below Kalsi. With its source in the 6,315 m high Bandarpunchh Mountain, it is the biggest tributary of the Yamuna. In fact, Tons carries more water than the Yamuna itself.