In Mongolia there are more than 400 smaller lakes covering a total area of about 1,450 km2. Numbers, sizes and volumes of lakes in floodplain areas changes with fluctuations of the flooding regime. Lakes in the Mongolian steppe and throughout the western part of the basin are characterized by dramatic fluctuations in volume and area. Often they are dry depressions, sometimes with salt marshes. The total area and volume of lakes and wetlands in Inner Mongolia and Mongolia also changes according to climatic cycles.
Barun-Torey Lake is located near the border between Russia and Mongolia in the Chitinskaya (Chita) Province of Russia. Its surface area is 550 km2, maximum depth 4.6 m, and volume 1.38 km3. Near Barun-Torey Lake is the smaller Zun-Torey Lake with a surface area of 285 km2, maximum depth of 6.76 m, and volume of 1.62 km3. During the last 200 years these lakes have nearly gone dry several times. Together with the Uldz River they form one of the endorheic basins that do not drain to the Amur-Heilong River.
Buir (Bei’erhu, Buyr Nuur) Lake is the largest lake in the Mongolia part of the Amur-Heilong basin and the fifth largest lake in Mongolia. The lake is located in the transboundary area of Mongolia and China and is fed by the Khalkh River. Water surface area of the lake is 615 km2, and maximum depth is 10.4 m. The lake basin area is 25,000 km2 and mean volume of the lake is 3.8 km3. In low flow years, mean depth is about 5.7 m with a volume of 3.5 km3. In high flow years the mean depth increases to nearly 7 m with a corresponding increase of volume to 4.3 km3. In China, the Orshun River originates from the lake delta and drains into Dalai Lake. And thus the northeastern part of lake water is fresher. Lake mineralization varies from 180 mg/l in a high flow year to 375 mg/l in a low flow year. Buir Lake is very rich in plankton, benthic invertebrates, and other aquatic biota and is one of the most biologically rich lakes in Mongolia. Twenty nine species of fish inhabit Buir Lake. In relative warm and high mineralization years fish reproduction increases significantly.
Dalai (Hulunhu, Dalainor) Lake is the 5th largest lake in China. It lies between Manzhouli City and Xinba’erhuzuoqi County west of the Hulunbei’er grasslands of Inner Mongolia. The lake is 93 km long, 447 km in circumference, 32 km in average width, and 41 km at its greatest width. In water abundant years it contains up to 14 km3 of water, with a surface area of 2,339 km2 and average depth of 5.7 m. The largest river tributaries of Dalai Lake are the Kherlen and Orxon. The Dalai basin covers about 200,000 km2 if the Kherlen, Khalkh and Oshun Rivers are considered together. The Mutnaya River, later substituted by the man-made Xinkaihe channel connects Dalai Lake to the Argun watershed, although lake discharge is insignificant to the volume of the Argun, and in dry periods ceases completely. Since 2000 the water levels of Dalai Lake have dropped sharply, suggesting that it might again dry up into a network of shallow pools, similar to the situation observed in 1904.
The Song-Nen Plain near the confluence of the Nen and Second Songhua Rivers has several dozen large and many thousand small shallow lakes that fluctuate in area and depth with climate cycles. Chagan Lake in Jilin Province is the largest one. Prior to the construction of flood-control dykes to contain the Songhua and Nen Rivers these lakes filled during floods and provided habitats for millions of migrating and breeding waterfowl. After flood control blocked the supply of flood waters from the main river channels, these floodplain lakes dried and were often converted to farmlands.