a river in Irkutsk Oblast, RSFSR; a left tributary of the Nizhniaia Tunguska River. It is 683 km long and drains an area of 19,100 sq km. The Nepa rises on the Angara Ridge and meanders through a deep valley. It is fed chiefly by snow. The mean flow rate measured at the village of Tokma on the river’s upper course is approximately 20 cu m per sec. The river freezes in October and thaws in the second half of May. Timber may be floated on the Nepa.