Wye, river of Wales and England. It rises on Plynlimon Mountain, Powys, flows 209 km (130 mi) in a generally south-eastern direction, and empties into the estuary of the River Severn near Chepstow. The tide sometimes rises 14 m (46 ft) at its mouth, above which the river is navigable by small vessels for 24 km (15 mi). The river flows through the spa town of Builth Wells in Powys, where it is joined by the Irfon before turning north-west on a meandering course through Hay-on-Wye, a small market town that has recently become a major centre of the second-hand book trade. From there the river continues westwards through Herefordshire and through the cathedral city of Hereford, where it is joined by the river Lugg. Here the Wye turns south, passing through Ross-on-Wye and Monmouth, Gwent, where it is joined by the Monnow and the Trothy. The lower course of the Wye from Monmouth to Chepstow is noted for its scenic beauty; the ruins of Tintern Abbey are on the river about 8 km (5 mi) from the river's mouth.