Zavkhan River is a river in Mongolia. It flows from Khangai Mountains to Lake Khyargas, and has a draining area of over 71,000 km². The river forms most of the border between the Govi-Altai and Zavkhan aimags. The length of the river is 670 kilometres. The river has recently gained publicity as a result of the activities of Salkhin Sandag Association - a local environmental organisation - to protect it and its surrounding areas.