It found its source on the north face of the Star Mounts and wound its way east and south through the Dire Wood. There it gained its name from the red tinge its waters took on as they passed the ruined city of Karse. By the time it joined the Delimbiyr, its waters returned to a normal hue.
It was said that drinking from the waters when they still flowed red could grant an increase to magical powers, or help stave off adverse magical effects. The red colour was attributed simply to soil deposits picked up as the river passed through the Dire Wood. However, other sources mentioned contamination from the blood of the still-beating heart of the dead god Karsus.