The River Wye is the fourth-longest river in the UK, stretching some 250 kilometres from its source on Plynlimon in mid Wales to the Severn Estuary. The lower reaches of the river forms part of the border between England and Wales. The Wye Valley is designated an Area of Outstanding Natural Beauty. The Wye is important for nature conservation and re…The River Wye is the fourth-longest river in the UK, stretching some 250 kilometres from its source on Plynlimon in mid Wales to the Severn Estuary. The lower reaches of the river forms part of the border between England and Wales. The Wye Valley is designated an Area of Outstanding Natural Beauty. The Wye is important for nature conservation and recreation, but is affected by pollution.