The Ider River (Mongolian: Идэр гол, Ider gol, or Идэрийн гол, Ideriyn gol, "Young River") is a river in the Khövsgöl and Zavkhan aimags in northwestern Mongolia and is, together with the Delger mörön river, one of the sources of the Selenga river. It is 452 kilometres (281 mi) long, and has a drainage basin of 24,600 square kilometres (9,500 sq mi). The source is in the Khangai range, the confluence with the Delgermörön is in Tömörbulag. The river is frozen 170–180 nights per year. There is a wooden bridge, which was built in 1940, near Jargalant and a concrete bridge in Galt.

• List of rivers of Mongolia