11 Facts About the River Thames

An aerial view of the river Thames at sunset.
An aerial view of the river Thames at sunset. / DieterMeyrl/Getty Images

The river Thames has been an integral part of the London story more than 2000 years. The winding ribbon of wildness snakes its way through the center of the British capital, continuing to waylay whales, inspire artists, sink ships, and occasionally flood areas of the city. It's old, yet constantly renewing, much like London itself.

1. The River Thames is a force of nature.

The Thames flows for 215 miles from its source at Trewsbury Mead in the Cotswolds to the North Sea, and its tidal flow stretches all the way from Teddington Lock to the Thames Estuary. The difference in water levels can be startling; its depths vary from 15 to 22 feet between low and high tide.

The Thames's strong currents carry more than 22,000 tons (some 20,000 tonnes) of sediment per tide, giving rise to its famously murky color. The routines of those who make their living on the waters are governed by tide tables, complex computations predicting the rise and fall of the water at particular stretches of the river.

2. London was founded because of the River Thames.

A depiction of Londinium in 120 CE.
A depiction of Londinium in 120 CE. / Carole Raddato, Wikimedia Commons // CC BY-SA 2.0

London owes its position to the Thames. The original Roman city was built at its most convenient bridging point, connecting the north bank to the marshes of Southwark, near the site of the current London Bridge. The river was much wider and shallower then. It flowed over and between a collection of islands and marshes, watered by a range of tributaries that have since been paved over. The Roman port was centered on the Walbrook, a tributary that was regularly engulfed by the waters of the Thames at high tide. A major excavation in 2013 found more than 10,000 artifacts here, including letters, pottery, and shoes.

3. The River Thames is the longest archaeological site in London.

Archaeologists and mudlarks—amateur archaeologists with a permit from the Port of London Authority—can often be seen down on the foreshore, bent over the sand, mud, and pebbles with a singular focus. Thanks to the push and pull of the tides, the river regularly offers up evidence of London’s long history. People have found ancient objects like Iron Age shields, Roman tiles, medieval clay pipes, and leather Tudor shoes. The foreshore at Vauxhall has revealed London’s history to be even longer than originally thought: In 2010, archaeologists discovered rare timber structures dating from the Mesolithic period, not far from the Bronze Age timber jetty discovered in the 1990s.

4. London Bridge was once the city's only bridge across the River Thames.

The Romans built the first bridge across the river in around 50 CE. The original wooden structure was rebuilt numerous times and remained the only bridge across the Thames in London until the opening of Westminster Bridge in 1750. The city’s watermen resisted the construction of new bridges, as their livelihoods depended on ferrying people across the river.

The medieval London Bridge, complete with shops, houses, a chapel, and a gatehouse topped with the heads of traitors displayed on spikes, was a marvel of engineering. Supported by 20 arches, it stood for some 600 years, and wasn’t dismantled until 1831 so a larger bridge could take its place.

5. Fairs were held when the River Thames froze.

A 1683 frost fair on the river Thames.
A 1683 frost fair on the river Thames. / Heritage Images/Hulton Archive/Getty Images

The first officially documented Frost Fair occurred in 1608, when the Thames froze for six weeks. Londoners took to the ice, playing games, roasting oxen, and drinking beer.

Back then, the Thames moved more slowly than today, enabling it to freeze more easily. The multiple arches supporting the old London Bridge were often blocked by ice and debris during the winter, further slowing the river. These Frost Fairs occurred in a period of cold weather known as the Little Ice Age, which inflicted Arctic winters on much of Europe from the 14th century to the mid-19th century.

But Frost Fairs became a thing of the past after the architecture along the Thames changed and the climate warmed. The new London Bridge that opened in 1831 had fewer arches, letting the water flow more easily. Meanwhile, the construction of the Embankment narrowed the river significantly, causing it to flow faster.

6. The River Thames was an extremely busy port.

Over the course of the 18th century, the volume of trade passing through London had nearly tripled. Commodities such as coal, rum, sugar, tea, and spices were in increasing demand but, to the consternation of merchants and ship-owners, the port was not set up to handle so much traffic. The port was so congested by the 1790s that nearly 2000 vessels had to moor in a space meant for 542. As a result, the early years of the 19th century saw a flurry of construction, with new docks and warehouses being built to accommodate the ever-increasing amount of commerce. With the arrival of steam, yet more docks, larger and deeper, were built downriver.

7. The River Thames Police is the world’s oldest police force.

The Thames Police has been patrolling the waters since 1798, making it the oldest continually serving police force in the world. The force has had plenty to do throughout their long history: The increase in trade and the chaotic conditions on the river meant there was ample opportunity for river pirates, night plunderers, and scuffle-hunters to make off with cargo. Losses from such theft amounted to around £500,000 a year.

At the request of the West India Committee, Scottish magistrate Patrick Colquhoun and Justice of the Peace John Harriott came up with a plan to police shipping on the Thames. The investment paid off: In the first year, the West India Merchants saved over £120,000 in stolen goods.

8. The River Thames has inspired various artists.

The Fighting Temeraire (1839) by J. M. W. Turner
The Fighting Temeraire (1839) by J. M. W. Turner / National Gallery of Art, Wikimedia Commons // Public Domain

Artists have long found inspiration in the murky waters and bustling foreshore of the Thames. The American artist James McNeill Whistler, who lived in London from 1859 until his death in 1903, was fascinated by the river and depicted it in numerous works. French artists such as Claude Monet, Camille Pissarro, and James Tissot, exiled to London during the Franco-Prussian War of 1870-71, were also moved to capture the play of light and dark on the waters. J. M. W. Turner’s art was intertwined with the Thames, shown most spectacularly in the depiction of an old gunship being towed downriver to be broken up in The Fighting Temeraire (1839).

9. Shipwrecks litter the riverbed of the River Thames.

The Thames is the last resting place of numerous ships and boats. Sunk by storm, human error, or enemy action, they lie immersed in the river’s silt, waiting to reveal their secrets.

One dramatic example is the so-called “Doomsday Ship,” the American Liberty Ship the SS Richard Montgomery. While laden with 7000 tons of munitions, the Montgomery ran aground on a sandbank in the Thames Estuary in August 1944 and broke up over the next few days. Half the cargo was removed, but once the ship flooded, further removal was declared too dangerous. The ship and its deadly cargo remain just below the surface, surrounded by an exclusion zone [PDF].

10. The Thames Barrier protects London from flooding.

A combination of high tides and storm surges from the North Sea means that flooding has always been a threat along the Thames. After the North Sea Flood of 1953 inundated Canvey Island and caused further casualties along England's East Coast, Scotland, the Netherlands, and Belgium, people began focusing their attention on flood defenses.

For London, the end result was the Thames Barrier, the second largest flood barrier in the world after the Oosterscheldekering Barrier in the Netherlands. Opened in 1984, its 10 gargantuan gates protect nearly 50 square miles (125 square kilometers) of central London from flooding caused by storm surges. As of June 2021, the Thames Barrier has been raised 199 times.

11. The River Thames has cleaned up its act.

The Thames is an ecological success story. Though declared biologically dead in the 1950s due to pollution, it is now a flourishing, if fragile, ecosystem, with 125 species of fish recorded. Surveys run by the Zoological Society of London have reported sightings of seals, porpoises, and dolphins along the course of the river. Whales have also been spotted, such as the minke whale calf found as far inland as Richmond—more than 90 miles from the sea—in May 2021.

But the health of the Thames is a work in progress. Plastic is the latest threat, along with sewage spillover. London’s sewer system—a marvel of Victorian engineering—is still in good shape, but it was built for a significantly smaller population. A 15-mile-long (25 kilometers) super sewer under the Thames is currently under construction.