Lake Khövsgöl (Mongolian: Хөвсгөл нуур, Khövsgöl nuur,:Kobsogol naghur.svg Höbsügül nagur), also referred to as Khövsgöl dalai (Хөвсгөл далай, Khövsgöl ocean) or Dalai Eej (Далай ээж, ocean mother) is the largest fresh water lake in Mongolia by volume, and second largest by area. Khövsgöl Nuur is nicknamed "Younger sister of the Sister Lakes (Lake Khövsgöl and Lake Baikal)".
Khövsgöl nuur is located in the northwest of Mongolia near the border to Russia, at the foot of the eastern Sayan Mountains. It is 1,645 m above sea level, 136 km long and 262 m deep. It is the second-most voluminous freshwater lake in Asia, and holds almost 70% of Mongolia's fresh water and 0.4% of all the fresh water in the World. The town of Hatgal is at the southern end of the lake.
Its watershed is relatively small, and it only has small tributaries. It gets drained at the south end by the Egiin Gol, which connects to the Selenge and ultimately into Lake Baikal. In between, the water travels a distance of more than 1,000 km, and a height difference of 1,169 m, although the line-of-sight distance is only about 200 km. Its location in northern Mongolia helps form the southern border of the great Siberian taiga forest, of which the dominant tree is the Siberian Larch (Larix sibirica),
The lake is surrounded by several mountain ranges. The highest mountain is the Bürenkhaan / Mönkh Saridag (3,492 m), which has its peak north of the lake exactly on the Russian-Mongolian border. The surface of the lake freezes over completely in winter. The ice cover gets strong enough to carry heavy trucks, so that transport routes were installed on its surface as shortcuts to the normal roads. However, this practice is now forbidden, to prevent pollution of the lake from both oil leaks and trucks breaking through the ice. It is estimated that 30-40 cars have sunk into the lake over the years.
Khövsgöl is one of seventeen ancient lakes worldwide more than 2 million years old and the most pristine (apart from Lake Vostok). and is the most significant drinking water reserve of Mongolia. Its water is potable without any treatment. Hovsgol is an ultraoligotrophic lake with low levels of nutrients and primary productivity and high water clarity (secchi depths > 18 m are common). Hovsgol's fish community is species poor compared to that of Lake Baikal. Species of commercial and recreational interest include Eurasian perch (Perca fluviatilis), burbot (Lota lota), lenok (Brachymystax lenok), and the endangered endemic Hovsgol grayling (Thymallus nigrescens). Though endangered by poaching during its spawning runs, the Hovsgol grayling is still abundant throughout much of the lake.
The Lake area is a National Park bigger than Yellowstone and strictly protected as a transition zone between Central Asian Steppe and Siberian Taiga. Despite Hovsgol's protected status, illegal fishing is common and prohibitions against commercial fishing with gillnets are seldom enforced. The lake is traditionally considered sacred in a land suffering from arid conditions where most lakes are salty. The Park is home to a variety of wildlife such as ibex, argali, elk, wolf, wolverine, musk deer, brown bear, Siberian moose and sable.
The Hövsgöl (Khövsgöl) Long-term Ecological Research Site (LTERS) was established in 1997 and an extensive research program began soon thereafter. Now, part of an international network of long-term study sites, the Hövsgöl LTERS provides a stage for nurturing Mongolia's scientific and environmental infrastructures, studying climate change and developing sustainable responses to some of environmental challenges facing the lake and its watershed.