The Sellyakh (Russian: Сыалах or Сельлях; Yakut: Сиэллээх, Sielleex) is a river in the Sakha Republic (Yakutia), Russia.

[1] The river flows north of the Arctic Circle, across territories of the Ust-Yansky District marked by permafrost.

The lower course of the river belongs to the Yana Delta Ramsar wetland site.

The Sellyakh flows roughly northwestwards across very swampy flatland dotted with small lakes, to the northeast of the Nuchcha.

Its channel meanders strongly and in its lower course the river turns north, its floodplain roughly parallel to the Chondon that flows northwards to the west.