The Thames
The Thames is the most famous river in Britain. It flows for 346 km from the Cotswold hills of southwest England through the capital city of London and out into the North Sea. For 2,000 years the Thames has been a working river, carrying goods, people and history. It is also one of the most successful clean-up stories in the world: a river that was once "biologically dead" is now one of the cleanest urban rivers anywhere.
- Length346 kmLongest river entirely in England
- CountryUnited KingdomEntirely in England
- SourceThames HeadA small spring in the Cotswolds
- MouthThe North SeaThrough a wide estuary east of London
- Bridges in LondonOver 30Including Tower Bridge and London Bridge
- WildlifeOver 125 fish speciesNow including seals and porpoises
The Thames compared to the world's great rivers
The Thames is short compared to the world's giant rivers but punches above its weight in history and culture.
What is the Thames?
The Thames is the longest river entirely within England. It begins as a small spring called Thames Head in the Cotswold hills of Gloucestershire and flows generally eastwards through Oxford, Reading and London before reaching the North Sea. The tidal Thames in London rises and falls with the tides up to 7 metres twice a day, and seawater pushes up the river as far as Teddington in west London.
The Great Stink
By the mid-1800s the Thames was a sewer. London had grown to two million people but had no proper sewage system. Most human waste went straight into the river. In the hot summer of 1858, the smell became so bad that Members of Parliament could not work in the Houses of Parliament beside the river. They called it the Great Stink. They quickly passed laws to fund the construction of London's first proper sewer system.
The engineer Joseph Bazalgette designed a network of 1,800 km of brick sewers that carried London's waste downstream and discharged it into the river east of the city. Bazalgette's sewers still serve London today. They saved thousands of lives by stopping the regular cholera outbreaks that had plagued the city.
The Thames Barrier
London sits on the tidal Thames and is at risk from huge storm surges driven inland by North Sea storms. In 1953 a great storm killed over 300 people on the east coast of England and only just missed London. To prevent a similar disaster from drowning the city, the Thames Barrier was built across the river in east London in 1982. It is a row of 10 huge steel gates that can be raised in 30 minutes to block surges of seawater.
The Thames Barrier is one of the largest moveable flood barriers in the world. It is currently raised approx. 6 to 10 times a year, but with sea levels rising and storms getting stronger, it may need to be replaced by 2070.
The Thames today
Today the Thames is busy with tourist boats, river buses, rowing clubs and the famous Oxford and Cambridge Boat Race. The river is crossed by over 30 bridges in London alone, including the iconic Tower Bridge (often confused with London Bridge) and the original London Bridge. The river also has the Tower of London, the Houses of Parliament, the London Eye, Tate Modern, the Globe Theatre, and many other famous sights on its banks.
Deeper dive: tidal estuary, Roman London and the Tideway super-sewer
The Thames is unusual among major capital-city rivers in being a tidal estuary for its lower 110 km, all the way from the North Sea up to Teddington Lock in west London. Twice a day, billions of litres of seawater flood up the river and then flow back out. The tidal range in central London is approx. 7 metres, which is why river-level walkways disappear under water at every high tide. The tidal nature of the river has shaped London's history and economy: the Pool of London (the stretch of river between London Bridge and Tower Bridge) was the busiest port in the world for much of the 18th and 19th centuries because ocean-going ships could reach it on a high tide.
The Romans founded the city of Londinium around 47 AD at the lowest crossable point of the Thames, where they built the first London Bridge near the location of the modern one. The river was important enough to defend with a wall around the city and a fleet on the river. Anglo-Saxon and Viking Londons all clustered along the same stretch. The river's name probably comes from a pre-Roman Celtic word meaning "the dark one", referring to the river's muddy colour.
Despite the success of Bazalgette's Victorian sewers, modern London grew far beyond what they were designed for. During heavy rainstorms, the system overflows and dumps tens of millions of cubic metres of raw sewage into the Thames every year. To fix this, the Thames Tideway Tunnel (the "super-sewer") was built between 2016 and 2024. It is a 25 km tunnel running deep beneath the river from Acton in west London to Beckton in east London. The tunnel intercepts sewer overflows and stops them from reaching the river. When it began operating in 2024, the volume of untreated sewage entering the Thames in central London was expected to drop by approx. 95%. The full benefit will take years to show up in fish populations, but the trajectory of the Thames clean-up over the last 70 years is one of the great urban environmental successes.
The country is the United Kingdom. The river system in Russia is the Volga.