Wye, river, c.130 mi (210 km) long, rising on Plynlimon Mt., W Wales, and flowing generally SE past Builth Wells (Wales), Hereford (England), and Monmouth (Wales) to the estuary of the Severn River. It is noted for its beautiful valley, especially the part that forms the Gloucestershire-Monmouthshire boundary. Reservoirs on the Elan River, a tributary, provide water for Birmingham.
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