page_title: River Thames
section_title: 20th century
hierarchical_section_title: River Thames / Human history / 20th century
context_page_description: The River Thames, known alternatively in parts as the Isis, is a river that flows through southern England including London. At 215 miles, it is the longest river entirely in England and the second-longest in the United Kingdom, after the River Severn.
  It flows through Oxford, Reading, Henley-on-Thames and Windsor. The lower reaches of the river are called the Tideway, derived from its long tidal reach up to Teddington Lock. It rises at Thames Head in Gloucestershire, and flows into the North Sea via the Thames Estuary. The Thames drains the whole of Greater London.
  Its tidal section, reaching up to Teddington Lock, includes most of its London stretch and has a rise and fall of 23 feet. Running through some of the driest parts of mainland Britain and heavily abstracted for drinking water, the Thames' discharge is low considering its length and breadth: the Severn has a discharge almost twice as large on average despite having a smaller drainage basin. In Scotland, the Tay achieves more than double the Thames' average discharge from a drainage basin that is 60% smaller.
  Along its course are 45 navigation locks with accompanying weirs.
context_section_description: The growth of road transport, and the decline of the Empire in the years following 1914, reduced the economic prominence of the river. During the Second World War, the protection of certain Thames-side facilities, particularly docks and water treatment plants, was crucial to the munitions and water supply of the country. The river's defences included the Maunsell forts in the estuary, and the use of barrage balloons to counter German bombers using the reflectivity and shapes of the river to navigate during the Blitz.
  In the post-war era, although the Port of London remains one of the UK's three main ports, most trade has moved downstream from central London. In the late 1950s, the discharge of methane gas in the depths of the river caused the water to bubble, and the toxins wore away at boats' propellers.
  The decline of heavy industry and tanneries, reduced use of oil-pollutants and improved sewage treatment have led to much better water quality compared to the late 19th and early- to mid-20th centuries and aquatic life has returned to its formerly 'dead' stretches.
  Alongside the entire river runs the Thames Path, a National Route for walkers and cyclists.
  In the early 1980s a pioneering flood control device, the Thames Barrier, was opened. It is closed to tides several times a year to prevent water damage to London's low-lying areas upstream (the 1928 Thames flood demonstrated the severity of this type of event).
  In the late 1990s, the 7-mile (11 km) long Jubilee River was built as a wide "naturalistic" flood relief channel from Taplow to Eton to help reduce the flood risk in Maidenhead Windsor and Eton.
caption: The Thames as it flows through east London, with the Isle of Dogs in the centre
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