The Bezdna (Russian: Бездна) or Biznä (Tatar Cyrillic: Бизнә, Latin: Biznä) is a river in Tatarstan, Russian Federation, a left-bank tributary of the Volga River, falling into the Kuybyshev Reservoir near Kuralovo, Spassky District. Its length is 45 km and its drainage basin is 806 km².
The maximal mineralization 300-500 mg/l. Average sediment in mouth per year is 129 mm. In 1963 average discharge was 197 m3/s. The town of Spassk, the ancestor of modern Bolgar stood on the river prior to 1956. In 1956-57 the Kuybyshev reservoir was created, flooding the town and the lower stream of Bezdna.