The River Gladden originated in the Misty Mountains and emptied into the Anduin in the Gladden Fields. In Sindarin the river was called Sîr Ninglor. There were yellow irises growing along the river and among the marshes of the Gladden Fields.

Its source was two streams flowing east from the Misty Mountains north of Khazad-dûm. The river flowed roughly halfway between the Carrock to the north and Lórien to the south.

While the river was only minor - being only around 100 miles in length, the Gladden played a great part in the histories of the Third Age. It was there that Déagol rediscovered the Ring, and there that Sméagol took the Ring.