Lake Hulunlake, China Chinese (Pinyin) Hulun Hu or (Wade-Giles romanization) Hu-lun Hu, Mongolian Hulun Nuur, also called Chalai Nor or Dalai Nor

large lake in the Hulun Buir Plain, northern part of the Inner Mongolia Autonomous Region, northern China. The lake is fed by two rivers that rise in Mongolia: the Kerulen (Kelulun), which flows from the west, and the Orxon (Orshun), which flows from the south.

The surface area of Lake Hulun has fluctuated considerably based on variations in the climate. At one time it was part of a large lake that included Lake Buyr (Buir)—a somewhat smaller body of water situated along the Chinese border just inside of Mongolia in the southern part of the Hulun Buir Plain—which drains into Lake Hulun via the Orxon River. Normally Hulun covers an area of about 894 square miles (2,315 square km). It is comparatively shallow and is joined by a seasonal channel to the Hailar River, which flows into the Argun River (the upstream portion of a tributary of the Amur River). For much of the year, however, it is undrained, and occasionally, when its level is at its lowest, there is a reverse flow of waters from the Hailar River into the lake. All of the rivers of this area are unstable, partly because of the concentration of rainfall in a short period of the summer and partly because of the great annual variations in the weather. Unlike most of the lakes in the Hulun Buir region, which are highly saline, both Lakes Hulun and Buyr have fresh water with a minimal salt content. Both are well-stocked with fish, which are consumed throughout the region. During the six months of bitter winter cold, most of the fish in Lake Hulun migrate up the Orxon River to Lake Buyr.