river rising from the glaciers on the southwestern slopes of the Altai Mountains in Sinkiang, China. It flows west across the Chinese border through Lake Zaysan, and then northwest across Kazakhstan to join the Ob River near Khanty-Mansiysk in Russian Siberia. The largest tributary of the Ob, the Irtysh is 2,640 miles (4,248 km) long and is navigable for most of its course. The Narym, Bukhtarma Om, and Tara are its chief right-bank tributaries, and the Osha, Ishim (Esil), Vagay, Tobol (Tobyl), and Konda are its main left-bank ones. The Öskemen hydroelectric station was completed in 1952 and that at Bukhtarma in 1960. The main river ports are Khanty-Mansiysk, Tobolsk, Tara, Omsk, Pavlodar, Semey, and Öskemen.