Bruinen or Loudwater is a river in eastern Eriador.
The Bruinen had only one point where it could be passed, a Ford near Rivendell. This Ford and by extension the river were called the Edge of the Wild.
At the beginning of the War of the Ring Frodo Baggins was raced on Glorfindel's horse towards the Ford of Bruinen, with the Ringwraiths in hot pursuit. At the Ford Frodo, poisoned by a deadly wound, made his stand, and defied the Lord of the Nazgûl. This lured the Ringwraiths into the Bruinen, and Elrond and Gandalf released a great flood, which took the form of horses made out of water due to Gandalf's magic. This flood killed the horses of the Ringwraiths and their physical forms, buying the Fellowship of the Ring some time.
Like most rivers in Eriador, the Bruinen had a Westron name, which Tolkien translated as Loudwater. Patrick H. Wynne linked the first element brui "noisy" to the second element of the word Ulumúri, and several other Qenya and Goldogrin words with some connection to "great sound". The second element is nen, "water".