Wanderlust World Wanderlust World The River Thames is 215 miles (346 km) long, making it the longest river entirely in England and the second-longest in the UK (after the Severn).
It rises at Thames Head near Kemble, Gloucestershire (Cotswolds), flows through Oxford, Reading, Henley, Marlow, Windsor, London, and empties into the North Sea via the Thames Estuary.
The tidal section (Teddington Lock to the sea) spans ~109 km and includes the iconic London stretch. The Thames Path National Trail follows the entire river.