|Location||Eriador west of Moria|
|Description||Lesser tributary of Glanduin|
|Other names||Gate Stream|
|Events||Journey of the Fellowship of the Ring to the South|
The Sirannon, or Gate Stream, was a stream in Eriador.
Beginning at the Silvertine, it flowed past the Doors of Durin, the gates of Moria (hence its name) to Ost-in-Edhil, the old capital city of the Noldor of Eregion, where it joined the river Glanduin. Along the river, from Ost-in-Edhil to Moria, ran an ancient road.
On 13 January T.A. 3019 (by which point both Moria and Eregion had long been abandoned), the Fellowship of the Ring found that the Sirannon had been dammed by someone or something, and before the gates of Moria there was now a foul lake. In this lake dwelt the Watcher in the Water, who nearly caught the Ringbearer Frodo Baggins.