Its source began in the Misty Mountains west of the River Rhimdath, and estimated at around one hundred miles north of Rivendell. It flowed through the Ettenmoors and then curved southward, skirting the western edge of the Trollshaws. Running under the Last Bridge on the East-West Road, it went on southward until it was joined by the River Bruinen or 'Loudwater'. The river then turned south-west until it met with the Glanduin, forming the fenland called Nin-in-Eilph or 'Swanfleet'. Beyond this point the combined waters were named Gwathlo.
Sometime around TA 1150, the Stoors came over the Redhorn Pass and settled in the Angle, the land between the Hoarwell and the Loudwater. When Angmar became powerful around TA 1300, these Hobbits moved over the Hoarwell to dwell near Bree.
In May TA 2941, Thorin and Company crossed the river on the Last Bridge and later on that same day they were waylaid by three trolls - Tom, Bert and William. Then, on 11th October TA 3018, Glorfindel the Elf-lord drove back the Nazgul from the Last Bridge and left a beryl in the mud in the middle of the road to show that the path ahead was safe. Two days later, after finding the elf-stone and knowing what it meant, Aragorn led the Hobbits Frodo, Sam, Merry and Pippin across the bridge on their way to Rivendell.