Rivers and Lakes
Asia's continental watershed runs through Mongolia, splitting the country's more than 4000 rivers and streams into three drainage basins. Roughly a quarter of Mongolia's territory lies in the Arctic drainage basin. This area includes the Selenge River drainage, (the major tributary of Siberia's famous Lake Baikal, which continues to the Arctic Ocean), the Shishkhed (west of Khovsgol Lake) and Bulgan rivers (in Khovd province). The rivers in a smaller area in northeastern Mongolia make up the Pacific drainage basin, including the Onon, Uldz, Kherlen, and Khalkhin Gol rivers, which flow east via Russia's mighty Amur River.
The majority of Mongolia's territory, however, drains to no ocean. Rather, it forms part of the vast Central Asian closed drainage basin. In the northwest, the basin encompasses the Depression of the Great Lakes, including Uvs Lake (Mongolia's largest lake by surface area), Khar Us Lake, Khar Lake, and Khyargas Lake. In central Mongolia, the basin includes the Valley of the Lakes between the Khangai and Gobi Altai mountains.
The lakes, rivers, streams, marshes, oases and other wetlands in each of the six preceding zones support their own distinctive flora and fauna. While the Arctic and Pacific drainage basins contain fish characteristic of those large drainages, the Central Asian closed drainage basin, ecologically isolated for centuries, contains an endemic and little studied species of fish called the Altai Osman (Oreoleuciscus potanini).
Wetlands provide crucial habitat for the waterfowl and water-frequenting birds that make up a majority of Mongolia's migratory bird species. Especially important to biodiversity are the huge reedy marshes bordering lakes in the Depression of the Great Lakes, and the dynamic floodplains of Mongolia's larger rivers.
Though they occupy a relatively small area of the country, riparian areas have great importance to the nation. Wetlands are both vital to nomadic livestock husbandry and vulnerable to impacts of high concentrations of people and animals near water.