(also Orog Nuur, Orok Nor), an undrained lake in the Mongolian People’s Republic, in the Valley of Lakes, in the northern foothills of the Gobi Altai. It lies at an elevation of 1,216 m, covers 130 sq km, and has a maximum depth of 4.5 m. The Tuin-Gol River flows into the lake.
The shores of the lake are low and sandy, with marshes or salt marshes in places. When rainfall is abundant the lake water is fresh; in dry years it is saline, and the lake is divided into pools. The lake is frozen from November to April. It is rich in fish and water fowl.