Khar-Us, meaning black water, is a freshwater lake situated south of the city of Khovd, at an elevation of 1,157 meters. It stretches 72 km long and 37 km wide. It is remarkably shallow: averaging between 2 and 4 meters in depth. It contains 3,432 cubic kilometers of water. It is the upper lake in an interconnected system of lakes, known as the Great Lakes depression.

The Khovd, Buyant and Tsenkher rivers flow into the lake, while the Chono Kharaikh river originates from it.

Khar-Us Lake presents distinctive geological features, with marshy shores overlooked by peaks crowned with eternal snow. In the middle of the lake sits the island of Ak-Bashi, meaning "white head" in the Kazakh language, which divides the lake into two sections: the South section and the North section. This island is situated 272 meters from the lake's edge.