Another name for the Loudwater.
The River Bruinen started out from the west of the Misty Mountains near the High Pass. It then flowed to the southwest and joined with the Hoarwell at The Angle.

The northern reaches of the Bruinen formed the western boundary of Rivendell and the depth and flow of the river could be manipulated by Lord Elrond of Rivendell. In the TA 3018 Lord Elrond, with the help of the wizard Gandalf, caused the river to rise violently and wash away the Nazgûl and their steeds when they attempted to cross the Loudwater and capture Frodo.
Encyclopedia entry originally written by Nienna-of-the-Valar