With a total length of 215 miles, the Thames is the longest river entirely in England. Rising at Thames Head in Gloucestershire and flowing through Oxford, Abingdon, Reading, Henley-on-Thames, Windsor, Kingston upon Thames, Richmond and Central London before flowing into the North Sea at the Thames Estuary. The river is tidal in Central London with a rise and fall of 23 ft and the catchment area covers a large part of Southern England. It is fed by over 20 tributaries and contains over 80 islands. The area upstream of Teddington Lock is tidal and is divided into reaches by 44 locks, which are manned during the daytime and user-operated at other times. This part of the river links to existing navigations at the River Wey and the Kennet and also the Oxford Canal. Our journey is upstream from Brentford on the tidal section in West London to Abingdon in Berkshire.