Table of Contents
- River Thames Quick Facts
- Where Does the River Thames Start?
- Where Does the River Thames End?
- So How Long Is the River Thames?
- How Old Is the Thames, Actually?
- Tidal vs Non-Tidal Thames
- Why Is the River Thames Brown?
- How Deep Is the River Thames?
- The River Thames Through London
- Wildlife in the Thames
- The History of the River Thames
- Culture, Literature and Art on the Thames
- What to Do on the River Thames
- Thames Events Worth Planning Around
- Why the River Thames Still Matters
- Thames FAQs
The River Thames is 215 miles of history, wildlife, weirs, bridges, rowing clubs and - if you time it wrong - some pretty strong tidal currents. It starts life as a trickle in a Gloucestershire meadow and ends up draining into the North Sea past container ships and saltmarsh. Along the way it flows through Oxford, Windsor, central London and some of the prettiest riverside towns in England.
Whether you're planning a walk along the Thames Path, want to get out on the water or just need the facts - here's what you'd actually want to know.
River Thames: The Numbers at a Glance
| Length | 215 miles (346 km) |
| Source | Thames Head, near Kemble, Gloucestershire |
| Mouth | Thames Estuary - North Sea |
| Locks (non-tidal section) | 45 |
| Bridges | 200+ |
| Islands | 80+ |
| Fish species | 125 in tidal Thames; 25+ in non-tidal |
| Thames Path | 296 km National Trail |
| Estimated age | 30-35 million years |
Where Does the River Thames Start (and Is There Actually a Debate About That)?
The traditional source of the River Thames is Thames Head - a field in the Cotswolds near the village of Kemble in Gloucestershire. And it's probably not what you're picturing. For most of the year it's just a meadow with a stone marker and barely any visible water, especially in summer when the ground absorbs everything before it can pool. There's a carved figure of Old Father Thames nearby, though the original statue was moved to St John's Lock near Lechlade years ago.
But there's actually a long-running argument about where the river really begins. Some geographers argue Seven Springs near Cheltenham is the proper traditional source, because that's where the River Churn rises. The Churn flows into the Thames near Cricklade, and by that measure the basin would be considerably larger. The official position sticks with Thames Head and that's what the Thames Path uses as its starting point - so that's the one most people go with.
The upper section gets its water from small streams and springs draining off the Cotswold hills, and it's pretty shallow for the first stretch - sometimes barely ankle-deep near the source. It picks up volume as it passes through Cricklade, Lechlade and Abingdon before becoming properly navigable.
One more thing worth knowing: once the Thames reaches Oxford, locals call it the River Isis. Same river, just a different name used for that particular stretch - something that confuses a fair few visitors who weren't expecting it.
The Source Marker at Thames Head
The nearest village to the source is Kemble, and it's a pretty easy walk from there. There's a stone marker on the site and if you're walking the Thames Path, this is officially where that journey starts. It's not dramatic - but there's something oddly satisfying about standing at the beginning of a 215-mile river that ends up flowing through the middle of London.
Where Does the River Thames End?
At the Thames Estuary, where it gradually widens and merges into the North Sea between Essex and Kent. That's the mouth of the river - and it's a pretty dramatic contrast to the quiet meadow it started in, 215 miles back to the west.
Before it gets there, the river flows through Oxford, Reading, Henley-on-Thames, Windsor and then the full length of London. It passes Old Windsor - the site of Runnymede, where the Magna Carta was signed - and picks up volume from its main tributaries along the way.
The Main Tributaries Worth Knowing
The Thames doesn't flow alone - it's fed by a whole network of other rivers and streams as it heads east:
- River Churn - joins near Cricklade; it rises at Seven Springs in Gloucestershire, which is why some geographers argue that's the real source
- River Kennet - joins at Reading and it's one of the larger tributaries. It's also navigable itself, connecting the Thames to the wider canal network heading west
- River Pang - joins near Pangbourne, a spot made famous by Jerome K. Jerome's Three Men in a Boat
- River Wey - joins near Weybridge, another navigable tributary with its own towpath
- River Mole - comes in near Molesey, downstream from Hampton Court
Each of these adds to the river flow and character. The Thames basin covers a large chunk of south-east England - it's a proper drainage system, not just one river.
So How Long Is the River Thames?
215 miles (346 km) - that makes it the longest river entirely within England. (The Severn's longer overall, but it flows through Wales too, so the "longest in England" title belongs to the Thames - depending on how you measure it, anyway.)
The Thames Path follows the river's full length from its Cotswolds source all the way to the Thames Barrier in east London - 296 km in total, slightly longer than the river itself because it winds along the banks rather than cutting straight across every bend. It's a National Trail and it's also the only river in Europe to have a national trail following its entire length, which is a genuinely impressive distinction. You can walk the whole thing end-to-end or just dip into sections at your own pace. Most people do the latter, and there's plenty to choose from.
How Old Is the Thames, Actually?
Old. Really old - somewhere around 30 to 35 million years by most geological estimates. But its present course is actually much more recent than that. During the last ice age, the upper Thames drained northeast into a completely different sea system. It's only around 450,000 years ago, when ice sheets pushed it south, that the river settled into the route it follows today.
A lot of the Thames basin sits pretty close to sea level, which is part of why the tidal section's so vulnerable to surge flooding - and it's the main reason the Thames Barrier exists.
Tidal vs Non-Tidal Thames - This Actually Matters
It's one of those things that doesn't come up much in general descriptions of the river, but it makes a real difference to what you're looking at and what you can do.
The dividing line is Teddington Lock - that's where the non-tidal river Thames ends and the tidal river begins.
The non-tidal Thames runs from the source down to Teddington. It's calmer and generally clearer - the water flow is managed by 45 locks and weirs that allow boats to navigate upstream and downstream. This is where most of the recreational boating and coarse fishing happens. The locks are maintained by the Environment Agency.
The tidal river runs from Teddington through central London and out to the estuary. It rises and falls by several metres twice a day with the tides - during high spring tides the water flow through central London can be surprisingly fast and the river looks completely different at low tide than at high tide. The tidal Thames is also where the water gets properly brackish - a mix of fresh water coming in river upstream and salt water pushing in from the sea. That combination supports 125 species of fish, including sea fish that wouldn't survive further upriver. And it's where you're most likely to spot dolphins, porpoises, seals and - yes - seahorses near Greenwich.
Why Is the River Thames Brown?
Not pollution, mostly. The brown colour comes from silt, clay and organic material stirred up from the riverbed - especially in the tidal section where the constant movement of tides keeps everything churned up. The estuary mud is thick, dark and centuries old. It's what gives the water that particular tea-coloured tint that surprises people expecting something clearer.
The upper non-tidal section's actually quite clear by comparison. Things get murkier as you move south and east toward London. Water quality's improved a lot since the 1950s - when the river was essentially biologically dead - but heavy rainfall still sometimes pushes sewage overflows in. It's recovered enough to support fish, seals, dolphins and seahorses, though, which says a lot.
How Deep Is the River Thames?
Depends where you're standing. The upper Thames can be knee-deep in dry summers - pretty shallow near the source. Around Oxford it averages about 1.5 to 2 metres.
In central London it's considerably deeper - around 7 to 10 metres at high tide, with some stretches deeper still. The estuary channels have been dredged for shipping and can reach around 30 metres in places. So the honest answer is: anywhere from not very deep to quite deep to seriously deep, depending on where you are and what the tides are doing.
The River Thames Through London - Bridges, Landmarks and Getting Around
A river Thames map with landmarks is basically a tour of London's greatest hits. The river curves through the city in a distinctive shape - that S-bend through central London is, oddly, something the Luftwaffe used as a navigation aid during the Blitz. Bomber pilots followed river shapes from the air at night and the Thames was easy to spot. Strange piece of trivia that doesn't come up much in tourist guides.
The Bridges (There Are More Than 200 of Them)
Some of the ones worth knowing:
- Tower Bridge - the gothic towers and lifting bascule mechanism date to 1894 and it still raises for tall ships passing through. Probably the most photographed bridge in England.
- London Bridge - the Romans built the original crossing roughly here. The medieval version had houses, shops and a chapel built on top of it - more like a crowded street than a bridge.
- Westminster Bridge - painted green to match the leather benches in the House of Commons. A genuinely odd design detail.
- Millennium Bridge - the pedestrian footbridge between St Paul's Cathedral and the Tate Modern. It famously wobbled when it opened in 2000 and had to close for two years. Perfectly stable now, and the views from it are good.
- Blackfriars Bridge - near where Benjamin Franklin finished his 1724 Thames swim from Chelsea. Yes, that Benjamin Franklin.
- Queen Elizabeth II Bridge - crosses near Thurrock in Essex, at one of the river's widest downstream points.
What You'll See Along the Banks in London
The South Bank's probably the best walking stretch in central London - St Paul's Cathedral and the Tate Modern on one side, the Houses of Parliament, Big Ben (the Elizabeth Tower, officially) and the London Eye on the other. Head east and you reach Greenwich, the Tower of London and Canary Wharf.
If you want a view from above, the Emirates Air Line cable car crosses the Thames between the Royal Docks and the O2 Peninsula near Greenwich - quick crossing, good views of the river from up there.
Battersea Power Station - now a shopping and residential complex - is on the north bank near Chelsea. Richmond and Kew are good options further west if you want calmer, greener riverside scenery.
Getting Around on the Water
River bus services run year-round between Putney in west London and Woolwich in the east - probably the most practical way to see the city from the water without paying full tourist-cruise prices. Plenty of tourist boats also run from central London past the Houses of Parliament, Tower Bridge and the Tower of London - a solid option if it's your first visit.
For a longer trip, passenger boats run the entire non-tidal river from Oxford down to Teddington. The full journey takes about four days and requires a few changes of boat - but if you've got the time, it's a pretty unhurried way to see the Thames Valley at your own pace.
The Thames Barrier
Near Woolwich in east London, the Thames Barrier sits across the river with 10 large steel gates that can be raised to stop tidal surges reaching central London. The city sits largely at or close to sea level, and without flood defences a serious storm surge from the North Sea could push water into huge areas of London. The Barrier's been raised over 200 times since it opened in 1982. It's managed jointly by the Environment Agency and the Port of London Authority.
Wildlife in the Thames - More Than Most People Expect
The river's ecological recovery is one of the better environmental stories of the last 70 years. In the 1950s the tidal Thames was officially declared biologically dead - no oxygen, no fish. Since then the water quality's improved enough that the river now supports:
- 125 species of fish in the tidal Thames - sea fish like bass and flounder coming in from the estuary, as well as freshwater species like perch, roach and pike in the non-tidal section
- Salmon and brown trout have been reintroduced and do appear in the river, though runs are still relatively modest
- European eels migrate all the way from the Sargasso Sea up into the Thames basin. They're an endangered species and the population is monitored by the Environment Agency
- Short-snouted seahorses have been found living near Greenwich - well upriver from the open sea, and a pretty striking sign of how much the habitat's recovered
- Dolphins and porpoises - harbour porpoises and bottlenose dolphins travel inland up the tidal Thames regularly, with sightings in central London more than once
- Grey seals and harbour seals - both species have been recorded in the Thames. The seal population in the Thames Estuary can reach up to 700 animals at certain times of year
- Swans - the subject of Swan Upping, an annual census conducted along the river every July between Sunbury and Abingdon. The swans are technically owned by the Crown, and the census has been running since the 12th century
And in 2006, a Northern Bottlenose Whale swam up the Thames all the way to central London. It made the front pages for days and didn't survive, but it was a pretty clear signal of how much the river's changed as a habitat.
The History of the River Thames (The Short Version)
How London Started Here
The Thames is the reason London became what it became. Around AD 47, the Romans established Londinium on the north bank - it was the lowest point where the river could be bridged, defensible from both sides and tidal enough for sea-going ships to reach. It grew into the provincial capital of Roman Britain, and its basic geography - a river city facing the estuary and the sea - hasn't really changed since. Evidence of human activity along the river goes back much further, though - there's archaeological evidence of people living along the Thames banks going back to Neolithic times.
The Magna Carta at Runnymede
In 1215, King John signed the Magna Carta at Runnymede - a watermeadow on the Thames near Old Windsor. It's one of the most significant moments in English legal history, establishing limits on royal power that eventually fed into constitutional law across much of the world. The site's still accessible today and managed by the National Trust.
The Great Stink of 1858
The most important moment in the river's modern history is probably the summer of 1858. London had been dumping raw sewage directly into the Thames for decades - while simultaneously drawing drinking water from it downstream. In the summer of 1858 the smell became so overwhelming that Parliament had to suspend its sittings. The curtains in the Houses of Parliament were soaked in chloride of lime just to make the building usable. They called it the Great Stink.
But something good came out of it. The crisis forced the construction of London's sewer system - designed by engineer Joseph Bazalgette, a network of 1,700 km of new sewers intercepting the outflows before they reached the river. It saved London from repeated cholera epidemics and parts of it are still in use. The Thames Tideway Tunnel - a 25 km deep tunnel beneath the river, completed in 2025 - is basically the 21st-century extension of that same project, handling the sewage overflows that still happen during heavy rainfall.
The Frost Fairs
Between roughly 1309 and 1814 the Thames froze solid enough in winter to hold fairs on the ice - stalls, games, ox roastings, even printing presses set up on the frozen river. The first recorded Frost Fair was in 1607 and the Great Frost of 1683-84 was one of the most severe, with the ice holding for around two months. The last Frost Fair was in 1814. After that, the old London Bridge - which had lots of small arches slowing the tidal flow and letting ice form - was replaced with a wider design. The river never froze again.
King Henry III's Polar Bear
In the 13th century, King Henry III received a polar bear as a gift from the King of Norway. It was kept at the Tower of London and - this really does sound made up - was regularly taken down to fish in the Thames on a long chain. A polar bear, on a lead, fishing in the river. One of those historical facts that's hard to improve on.
Culture, Literature and Art on the Thames
Kenneth Grahame walked the upper Thames for years and it fed directly into The Wind in the Willows (1908) - the messing about in boats, the riverbank picnics, the lazy summer afternoons. Mapledurham House near Pangbourne is thought to be the model for Toad Hall. The Oxford-to-Reading stretch of the river still feels a lot like the book describes it.
Jerome K. Jerome wrote Three Men in a Boat (1889) as a comic account of a trip upriver. It ends at the Swan Inn in Pangbourne, a pub that's still there today. Worth stopping for a pint if you're on the Thames Path.
Claude Monet visited London repeatedly between 1899 and 1905 and painted the Thames obsessively - over 100 canvases of the river in fog, haze and twilight. The Houses of Parliament, Waterloo Bridge, Charing Cross Bridge in all kinds of light. They're among the best-known examples of French Impressionism.
And in 1977, the Sex Pistols performed "God Save the Queen" on a boat called the Queen Elizabeth Riverboat, sailing past the Houses of Parliament on the Thames. They got arrested when the boat docked. It's one of the more theatrical moments in the river's history, and there's been nothing quite like it since.
What to Do on the River Thames
Out on the Water
The Thames has kayaking, canoeing, paddleboarding, sailing and rowing - with clubs and hire operators covering most of it along various stretches. The non-tidal river between the Cotswolds and Teddington is better for beginners and leisure paddling - no tidal surge, and the weirs and locks give you natural stopping points. The River Kennet and some other tributaries connect the Thames into the wider canal network if you want to extend a boat trip further afield.
There are over 200 rowing clubs along the river - from small clubs on the upper Thames to big London clubs. If you want to get into rowing, there's a club somewhere on the Thames that'll sort you out.
For something a bit different, dinner cruises run most evenings out of London - you get a meal and the city from the water at the same time. It's a genuinely different way to see central London at night.
Walking the Thames Path
The Thames Path runs from Thames Head in Gloucestershire all the way to the Thames Barrier in east London - 296 km total, all waymarked. It passes through market towns, alongside locks and weirs, through riverside villages and eventually into London's suburbs. Some of the best day-walk sections are around Henley-on-Thames, between Windsor and Maidenhead and the west London stretch from Richmond to Putney.
And it's worth knowing it's the only river in Europe with a national trail following its entire length - so if you're going to walk a river path, this is a pretty good one to pick.
Longer Boat Trips
Passenger boats run the full non-tidal river from Oxford to Teddington, taking about four days with a few changes of boat - a slow, pleasant way to see the Thames Valley. For privately hired boats, Penton Hook Marina near Staines is one of the bigger centres on the middle Thames and a good base for exploring that stretch at your own pace.
The 80+ Islands
The Thames has more than 80 islands scattered along its length - from large estuarial marshlands near the mouth to small wooded islets on the upper river. Some are reachable on foot by footbridge, others only by boat. Most are just trees and wildlife. Eel Pie Island in Twickenham hosted rock concerts in the early 1960s and is now home to a community of artists - the kind of place that doesn't come up much in mainstream travel guides, which is part of the appeal.
Fishing the Thames
The Thames is a decent coarse fishing river - barbel, chub, perch, bream, roach and pike are all present in the non-tidal section. Barbel grow large in the Thames and the river draws serious specimen hunters. The tidal section has sea species like bass, flounder and smelt moving through. A rod licence from the Environment Agency is required before fishing (for anglers 13 and over, available online). Good stretches include around Henley-on-Thames, Wallingford and Kingston-upon-Thames.
Eating Along the River
There are restaurants and riverside pubs all the way along the Thames - from village pubs on the upper river to proper dining with river views in London. The South Bank has a good concentration of options in central London, Richmond's riverfront is particularly worth a look and most of the market towns along the non-tidal Thames have at least one decent pub on the water.
Thames Events Worth Planning Around
Henley Royal Regatta - July, Henley-on-Thames. One of the most well-known rowing events in the world. The town fills up completely and the atmosphere on the riverbanks is genuinely something.
The Oxford and Cambridge Boat Race - spring, tidal Thames between Putney and Chiswick. Running since 1829. Hundreds of thousands of people line the banks to watch and it's free.
Swan Upping - July, Sunbury to Abingdon. The annual census of mute swans, conducted by the Royal Swan Uppers and two Livery Companies, travelling by traditional wooden skiffs. Been going since the 12th century. One of the stranger and more charming things you'll see on the Thames.
The World Poohsticks Championship - Sandford Lock near Oxford. Teams drop sticks from a bridge and race them downstream. Properly sanctioned, completely charming and taken about as seriously as it deserves to be.
Why the River Thames Still Matters
Historically, the Thames is why London became what it became - the lowest bridgeable point on the river, accessible to sea-going ships and at the centre of trade routes connecting Britain to Europe. The Port of London was for centuries one of the busiest in the world and the river still carries over five million tonnes of cargo annually - the busiest inland waterway in Britain.
Today it's a bit of everything at once. It's a water supply - Thames Water extracts and treats river water for millions of homes across south-east England. It's a transport route through the city. It's a wildlife habitat that's genuinely recovered from near-total ecological collapse. And it's a cultural centre for London in a way that's basically impossible to separate from the city's identity.
The Thames Barrier keeps central London from flooding. The Environment Agency and Port of London Authority jointly manage navigation, fishing and flood risk. And the river itself just keeps doing what it's done for 30-odd million years - running east from the Cotswold hills toward the sea.
Tourist's FAQ
How long is the River Thames?
215 miles (346 km) from Gloucestershire to the North Sea - the longest river entirely within England.
Where does the River Thames start and finish?
Officially it starts at Thames Head near Kemble in Gloucestershire and ends at the Thames Estuary into the North Sea. Some argue Seven Springs is the real source, where the River Churn rises - but Thames Head's the official one.
How deep is the River Thames?
It varies a lot - shallow enough to paddle through in places near the source, averaging 1.5-2 metres around Oxford, 7-10 metres in central London at high tide and up to 30 metres in dredged estuary channels.
Why is the River Thames brown?
Silt, clay and organic material stirred up from the riverbed - especially in the tidal section. It's not primarily a pollution issue, though water quality is still improving.
Can you drink Thames water?
Not straight from the river. But Thames Water extracts, treats and distributes it as drinking water to millions of homes across south-east England - so quite a lot of Londoners are drinking treated Thames water every day without really thinking about it.
How old is the River Thames?
Around 30-35 million years old, though its present course only settled into place about 450,000 years ago after the last ice age pushed it south.
Can you swim in the Thames?
Wild swimming's fairly common in the non-tidal upper Thames, particularly around the Cotswolds and Oxfordshire. The Port of London Authority officially discourages it in the tidal Thames through London though - the boat traffic and tidal currents make it genuinely risky. Always check water quality data before getting in anywhere.
What's the source of the River Thames?
Thames Head, a meadow near Kemble in Gloucestershire. There's a stone marker on the site and it's walkable from the village. It's also the start of the Thames Path.