a river in the Altai, in Altai Krai, RSFSR. It joins with the Katun’ to form the Ob’ River. It is 301 km long and has a basin area of 37,000 sq km. It flows from Lake Teletskoe.

In its upper course the Biia flows in a narrow valley and has rapids; below the mouth of the Lebed’ River, the valley broadens. The Biia is fed mainly by snow and rain, and it has a long flood period. Its average flow year-round is 477 cu m per sec (near the city of Biisk). Its upper course freezes over in late November or early December. (In some areas it does not freeze every year.) In its lower course it freezes in mid-November. The Biia thaws in the beginning of April in its upper course and in the middle of April in its lower course. It is used for floating timber. There is regular steamship service to Biisk, about 200 km from the mouth at high water.