structural:summarization
20th century

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 11 km (7 mi) 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, although it appears to have increased flooding in the villages immediately downstream.