The region of mountainous Bayan Ögliy included in this website’s inventory is drained by six systems of rivers and lakes, all rising in the snows and glaciers of Tavan Bogd or at the high ridges marking the boundaries of Mongolia with Russia and China. These systems, comprising an area of 21, 211 sq km, form drainages or basins and may be identified by their principle rivers or lakes: Sogoo Gol, Oigor Gol, Tsagaan Gol, Khoton and Khurgan Nuur, Dayan Nuur, Sagsay Gol, and the largest of all, that of Khovd Gol. Ultimately all these rivers and lakes drain into Khovd Gol, the longest river in western Mongolia.