THAMES BARRIER The Thames Barrier The world's largest movable flood barrier, spans 520 meters (a third of a mile) across the Thames at Woolwich Reach, South East London, The Barrier was built to protect the capital from the river flooding its banks until the year 2030 The Thames Barrier Visitors Centre on the South Bank is open daily. BOAT SERVICES TO THE BARRIER FROM GREENWICH PIER. Campion Launches: Tel. (+44) 181 305 0300 Fax: (+44) 13224 37175