The Selennyakh (Russian: Селеннях; Yakut: Силээннээх, romanized: Sileenneex) is a river in Sakha Republic, Russia.

The area of its drainage basin is 30,800 square kilometres (11,900 sq mi).

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.

[2] According to the State Water Register of Russia, it is a part of the Lena basin district.