The Thames rises from a field in Gloucestershire, runs 215 miles east through Oxford, Reading and Windsor, and reaches the sea beyond London. It is not Britain’s longest river — the Severn is — but it is by a wide margin its most consequential.
Say it right
TEMZ. The “h” is silent and the “a” is short. The spelling is a piece of Renaissance showing-off: scholars inserted the “h” to make the name look more classical, and nobody ever adjusted the pronunciation to match.
Why London is where it is
The Romans founded Londinium at the first point upstream where the river was narrow enough to bridge but still deep enough for seagoing ships. That single piece of geography made the city, and the Thames was its highway — for centuries the fastest way across London was by boat, and watermen ferried passengers the way taxis do now.
The Great Stink
By the 1850s London was pouring untreated sewage straight into the river. In the hot summer of 1858 the smell became so overpowering that Parliament — sitting directly on the bank — hung curtains soaked in chloride of lime at the windows and debated moving out of London entirely.
The result was one of the great feats of Victorian engineering. Joseph Bazalgette built 1,100 miles of sewers intercepting the waste and carrying it downstream, and deliberately specified pipes twice the diameter his calculations required. That decision is why his system, opened in the 1860s, still serves a city several times the size he designed it for.
Coming back to life
The Thames was declared biologically dead in 1957 — no fish, no oxygen. Sustained cleanup has brought it back: over 125 species of fish now live in it, along with seals, porpoises and the occasional lost whale. It is now often described as one of the cleanest rivers running through a major city, though sewage discharges after heavy rain remain a live scandal, and the Tideway “super sewer” was built to address exactly that.
The tide
The Thames is tidal as far upstream as Teddington Lock, with a range in central London of up to seven metres — one of the largest of any city river in the world. Flooding was a genuine and repeated threat until the Thames Barrier opened in 1982; it has closed over 200 times since, and its use is rising.
Things that happen on it
- The Boat Race — Oxford against Cambridge over four miles from Putney to Mortlake, rowed since 1829.
- Swan Upping — the annual royal census of swans, conducted in skiffs by men in scarlet.
- Mudlarking — searching the foreshore at low tide for objects the river has held for centuries. A permit is required.