Unzha River (Russian: Унжа), a river in the Vologda Oblast and Kostroma Oblast in Russia, a tributary of the Volga River. It is 426 kilometres (265 mi) long, and its basin covers 28,900 square kilometres (11,200 sq mi). The Unzha River begins at the confluence of the Kema River and the Lundonga River. It flows into the Unzhensky Cove of the Gorkovsky Reservoir. The Unzha River freezes up between October and December and stays under the ice until April or May. The main tributaries are the Viga, Neya, and the Mezha .