The rivers of Mongolia belong to the inland catchment basins of the Arctic Ocean, the Pacific Ocean and Central Asia Inland Basin. The higher and middle Selenge, the biggest river in the country and part of the Yenissei river belongs to the Arctic Ocean drainage basin.

In the northern and western mountainous parts of Mongolia, the water network is of high density. The southern central and south eastern parts of the country have a few rivers and other water resources and they are usually situated in depressions without any outflows.

Mongolia has numerous saltwater and freshwater lakes, which are great for camping, watching bird life, hiking, swimming and fishing.  The Great Lakes Depression is situated in the eastern part of the Mongolia Altai and consists of a few hollows with bigger lakes. The largest is the low-lying, saltwater lake Uvs Nuur (covering an area of 3.350 sq.km). The most popular is the magnificent Khovsnol Nuur (2,620 sq.km), the largest fresh-water lake in Central Asia, which contains 65% of Mongolia's (and 2% of the world's) fresh water

The Orhon (1,124 kilometers), the Herlen (1,090 kilometers) and the Selenge (539 kilometers) are the largest rivers.  On the north slope of Khangai mountains, there is the source of the Selenge Gol, Mongolia's largest river, which flows northward into Lake Baikal in Siberia. While the river Selenge gol is the largest in terms of water volume, the longest river is the Kherlen Gol in eastern Mongolia.

 Other geological and geographical features include underwater and above-ground caves, some with ancient rock paintings; dormant volcanoes: hot and cold mineral springs; the Great Lakes Depression in western Mongolia, the Darkhadyn Khotgor depression west of Khovsgol Nuur, and the Orkhon Khurkhree waterfall.  There are waterwalls in the rivers with the source from the Khangai Mountain range. The valley of the rivers is rich in rapids and waterwalls, which occur frequently. The Ulaan Tsutgalan Waterfall on the River Orkhon is one of the biggest Waterfalls in Mongolia.

Bulgan River

A strip of land supporting a beaver population between Bulgan soum and Bulgan River of Khovd aimag was initially designated as a protected area by PGH Presidium Resolution No. 17 (1965) in order to protect the beaver and its habitat. In 1995, it was included in the classification "nature reserve" with a territory measuring 1,840 hectares by Parliament Resolution No. 26, in accordance with the Law on Special Protected Areas. Various types of wildlife species inhabit this area. It is also home for very rare wildlife species such as beaver, silver-tipped black sable, stone marten, Mongolian agama, and more.

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