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a river in the Mongolian People’s Republic and Chita Oblast of the RSFSR. It merges with the Ingoda River to form the Shilka, one of the headwaters of the Amur. It is 1,032 km long and drains an area of 96,200 sq km. The Onon originates in central Khentei and flows through the Khentei-Chikoi Upland, where there are islands in the river. In its lower reaches the Onon flows between the Mogoituiskii and Borshchovochnyi ranges. It is fed mainly by snow; high water occurs in summer. At 12 km from its mouth the river discharges at a rate of 191 cu m per sec; the maximum discharge is 2,810 cu m per sec, and the minimum is 1,220 cu m per sec. The Onon freezes in November (the shoals are frozen solid), and the ice breaks up in April or early May. The main tributaries are the Hurakh-Gol, Borzia, and Unda (from the right) and the Agutsa, Kyra, and Aga (from the left). The Onon is used for irrigation and industrial purposes.