The river Erui occurs in J. R. R. Tolkien's fictional universe of Middle-earth.

The river Erui was one of the rivers which arose in the Middle-earth. It was not counted amongst the Seven Rivers of Gondor.

The river began near Mount Mindolluin in the White Mountains, flowing south through the province of Lossarnach, where it met the Anduin about 100 Númenórean miles south of Minas Tirith.

During the Kin-strife of Gondor, the Battle of Erui was fought at the Crossings of Erui that lied on the way to Pelargir.