Khar-Us Lake (Mongolian: Хар-Ус нуур, romanized: Har-Us nuur; ᠬᠠᠷ᠎ᠠᠤᠰᠤᠨᠠᠭᠤᠷ, "Black-Aqua Lake", is a lake in western Mongolia in the Great Lakes Depression. It is the upper one in a system of the interconnected lakes: Khar-Us, Khar, Dörgön, Airag and Khyargas. The lake is located in Har Us Nuur National Park.

Its area value (1,852 km) includes the island Agbash (or Ak-Bashi, white head) area (274 km), so the water surface area is 1,578 km only.

Some sources are using different Khar-Us Lake Lake statistics values:

• Water level: 1,160.08 m
• Surface area: 1,496.6 km
• Average depth: 2.1 m
• Volume: 3.12 km.

Water balance of Khar-Us Lake
(Unit of water balance: mm/year)

Surface input		Surface output		Groundwater inflow- outflow	Retention time, years
Precipitation	Inflow	Evaporation	Outflow
56.4	1,979.2	942.7	675.3	-417.6	1.1

Primary inflow is the Khovd River, which creates a large river delta.

So called Genghis Khan's wall runs along the western shore of the Khar-Us Lake. It is possible to find it at the Google Map and Google Earth satellite maps 47°53′29″N 91°59′37″E / 47.89139°N 91.99361°E / 47.89139; 91.99361.