In J. R. R. Tolkien's fictional Middle-earth, the Celduin or River Running was a 600-mile long river that ran from the Lonely Mountain south through the Long Lake where it was joined by the Forest River and thence through the easern outskirts of Mirkwood, then south east through apparently uninhabited regions of Rhovanion to its confluence with the Carnen and finally in a long south-eastward loop to the great inland Sea of Rhûn.
