The Selennyakh (Russian: Селеннях; Yakut: Силээннээх, romanized: Sileenneex) is a river in Sakha Republic, Russia. It is a left tributary of the Indigirka.

The length of the river is 796 kilometres (495 mi). The area of its drainage basin is 30,800 square kilometres (11,900 sq mi).

It originates in the north-west of the Chersky Range. The river flows southeastwards through the Moma-Selennyakh Depression which is bound in this area by the Burkat and Khadaranya ranges, and in the east by the Selennyakh Range, then the river flows across the Ust-Yansky District, where Sayylyk, the only inhabited place of its basin is found.

In its middle course the Selennyakh makes a wide bend northeastwards and then flows across the Aby Lowland in a roughly eastern direction until it reaches the left bank of the Indigirka. The Selennyakh is frozen between October and May.

According to the State Water Register of Russia, it is a part of the Lena basin district. The average annual discharge in the mouth is 180 cubic metres per second (6,400 cu ft/s).

• Geography - Yakutia Organized