river in Krasnoyarsk kray (region) and Tomsk oblast (province), Russia, and the longest right-bank tributary of the Ob River; it is 1,118 miles (1,799 km) long and has a basin of 53,400 square miles (134,000 square km). The Chulym, formed by the convergence of the Bely and Chyorny Iyus, rises on the northeastern slopes of the Kuznetsky Alatau Mountains. It flows northward through the mountains and then westward and northwestward across the West Siberian Plain to join the Ob. In its lower course, which is navigable, it is characterized by numerous lakes and meanders. Its main tributaries are the Serezh, Uryup, Kiya, Bolshoy Uluy, and Kemchug.