River Monnow

The River Monnow (Welsh: Afon Mynwy) marks the England–Wales border for much of its 42 miles (68 km) length. After flowing through southwest Herefordshire, England, and eastern Monmouthshire, Wales, its confluence with the River Wye is approximately 1⁄3 mile (0.54 km) south of Monmouth.

The Monnow rises near Craswall on Cefn Hill just below the high Black Mountains, Wales. It flows southwards, gaining the waters of its tributaries the Escley Brook and Olchon Brook near Clodock and the waters of the River Honddu, from the Welsh side of the Black Mountains, near Pandy. The river then flows briefly eastwards, to Pontrilas, where it is joined by its largest tributary, the River Dore before again turning southwards. At Monmouth, the Monnow joins into the River Wye with the River Trothy. The unique medieval Monnow Bridge in Monmouth is the only remaining fortified river bridge in Great Britain with its gate tower standing on the bridge.

The 40 miles (64 km) long-distance Monnow Valley Walk follows the river.