River Tavy  The Tavy () is a river on Dartmoor, Devon, England. The name derives from the Brythonic root "Tam", once thought to mean 'dark' but now generally understood to mean 'to flow'. It has given its name to the town of Tavistock and the villages of Mary Tavy and Peter Tavy. It is a tributary of the River Tamar and has as its own tributaries:  At Tavistock it feeds a canal running to Morwellham Quay. Its mouth is crossed by the Tavy Bridge which carries the Tamar Valley railway line. The river is navigable inland as far as Lopwell, where a weir marks the normal tidal limit, about a journey from North Corner Quay at Devonport. River transport was an important feature of the local farming, mining, tourism and forestry economies. The Queen's Harbour Master for Plymouth is responsible for managing navigation on the River Tavy up to the normal tidal limit.