The growth of road transport and the decline of the Empire, in the years following 1914, reduced the economic prominence of the river. During World War II the protection of the Thames was crucial to the defence of the country. Defences included the Maunsell forts in the estuary and barrage balloons to cope with the threat of German bombers using the distinctive shape of the river to navigate during The Blitz. Although the Port of London remains one of the UK's three main ports, most trade has moved downstream from central London. The decline of manufacturing industry and improved sewage treatment have led to a massive clean-up since the filthy days of the late 19th and early- to mid-20th centuries, and aquatic life has returned to its formerly 'dead' waters. Alongside the river runs the Thames Path, providing a route for walkers and cyclists.
In the early 1980s a massive flood-control device, the Thames Barrier, was opened. It is closed several times a year to prevent water damage to London's low-lying areas upstream (as in the 1928 Thames flood for example). In the late 1990s, the 7-mile (11 km) long Jubilee River was built, which acts as a flood channel for the Thames around Maidenhead and Windsor.
The Thames is popular for riverside housing whether in high rise flats in central London or chalets on the banks and islands up stream. The river has its own residents dwelling on houseboats, typically around Brentford and Tagg's Island
One of the major industries on the river now is tourism. In London there are many sightseeing tours in tourist boats, past the more famous riverside attractions such as the Houses of Parliament and the Tower of London as well as regular riverboat services provided by London River Services. Along the course of the river a number of small private companies offer river trips at tourist sites such as Hampton Court, Windsor and Oxford. Many companies also provide boat hire and accommodation on the river.
The leisure navigation and sporting activities on the river have given rise to a number of dependent businesses including boatbuilding, marinas, ships chandlers and salvage services.
The river is policed by five police forces. The Thames Division is the River Police arm of London’s Metropolitan Police, while Surrey Police, Thames Valley Police, Essex Police and Kent Police have responsibilities on their parts of the river outside the metropolitan area. There is also a London Fire Brigade fire boat on the river. The river claims a number of lives each year. As a result of the Marchioness disaster in 1989 when 51 people died, the Government asked the Maritime and Coastguard Agency, the Port of London Authority and the Royal National Lifeboat Institution (RNLI) to work together to set up a dedicated Search and Rescue service for the tidal River Thames. As a result, there are four lifeboat stations on the river Thames based at Teddington, Chiswick Pier, Tower Pier and Gravesend.
The Thames is navigable from the estuary as far as Lechlade in Gloucestershire. Between the sea and Teddington Lock, the river forms part of the Port of London and navigation is administered by the Port of London Authority. From Teddington Lock to the head of navigation, the navigation authority is the Environment Agency. Both the tidal river through London and the non-tidal river upstream are intensively used for leisure navigation. All craft using the river Thames must be licensed.
The river is navigable to large ocean-going ships as far upstream as the Pool of London and London Bridge. Today little commercial traffic passes above the docks at Tilbury and central London sees only the occasional visiting cruise ship or warship, moored alongside HMS Belfast. There is a regular traffic of aggregate or refuse vessels, operating from wharves in the west of London. The tidal Thames links to the canal network at the River Lea Navigation, the Regent's Canal at Limehouse Basin, and the Grand Union Canal at Brentford.