(also Bol’shoi Tui), a river in Omsk Oblast, RSFSR; a right tributary of the Irtysh, in the Ob’ Basin. The Tui is 507 km long and drains an area of 8,490 sq km. It meanders through a marshy plain and has a width of up to 120 m in its lower course. Fed by mixed sources, primarily snow, it has a mean flow rate of 27.6 cu m per sec 61 km from its mouth. The Tui freezes in late October or the first half of November, and the ice breaks up in late April or the first half of May.