The Gusinaya (; , Xaastaax) is a river in the Sakha Republic (Yakutia), Russia. It has a length of and a drainage basin area of .
The river flows north of the Arctic Circle, across territories of the Allaikhovsky District marked by permafrost. There are no settlements along its course, only some hunting huts.
The Gusinaya has its sources in the southeastern shore of Empe-Talalakh (ÃÂüÿõ-âðûðûðà) lake of the northern end of the Yana-Indigirka Lowland, East Siberian Lowland. The river flows roughly southeastwards across partially swampy tundra until the confluence of the long Alyn-Ergiter-Salaata (ÃÂûÃÂý-ÃÂÃÂóøÃÂÃÂÃÂ-áðûððÃÂð), after which it turns eastward. Its channel meanders strongly all along among numerous lakes, some of them quite large. In the lower course the river divides into channels and turns southeast and then northeast, before emptying into the Gusinaya Bay of the East Siberian Sea to the south of the mouth of the Volchya.
The main tributaries of the Gusinaya are the long Chaikhana (çðùàðýð) and the long Mutnaya (ÃÂÃÂÃÂýðÃÂ) on the right. There are about 3,000 lakes in the basin, totaling an area of . The river is frozen between the beginning of October and mid June.