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Hambleden Lock is a lock with a long weir situated on the River Thames. The lock is on the Berkshire bank between Aston and Remenham. It was built by the Thames Navigation Commission in 1773.
The great weir is impressive and there are walkways over it from the lock to the small village of Mill End on the Buckinghamshire bank.
Wikipedia: Link

The River Thames rises at Thames Head in Gloucestershire ST9899 on the slopes of the Cotswolds and flows generally eastward to its mouth near Southend in Essex. At 215 miles long it is the second longest river in Britain after the Severn, and the longest entirely within England. Link