In J.R.R. Tolkien’s The Lord of the Rings, the river crossed by the Fellowship at Rivendell is the Bruinen.
The Bruinen, also called the Loudwater, flows through the valley of Rivendell. The Fellowship crosses it when leaving Elrond’s refuge and traveling south toward the mountain pass of Caradhras. At the river’s ford, the Nazgûl pursue Frodo and the other travelers.
Elrond causes the river to rise against the Ringwraiths. The resulting flood carries away the pursuing horses and overwhelms the Nazgûl, although Frodo is badly wounded by the Witch-king before reaching the crossing. This event is one reason Rivendell provides such an important temporary sanctuary.
The Anduin is the Great River of Middle-earth and is crossed later in the journey. The Isen flows through Rohan, while the Baranduin, or Brandywine, borders parts of the Shire.