either of two roughly parallel rivers of western Siberia, Russia, both tributaries of the Yenisey. Both rivers flow generally northwest, but the Podkamennaya Tunguska River turns west at about 62° N to join the Yenisey, whereas the Nizhnyaya Tunguska River continues its northwestward course to about 66° N before flowing west to the Yenisey. See also Nizhnyaya Tunguska River; Podkamennaya Tunguska River.