On a sweltering summer day on the South Bank, do you ever find yourself looking wistfully at the Thames and wonder – can I just go in for a refreshing dip? Sure, it looks a bit muddy, but I heard it’s actually perfectly clean. Or is it?

So let’s answer the question: can you swim in the Thames?

Swimming in the Thames: the short answer

Short answer: yes – BUT, it’s strongly discouraged. And I mean, really strongly. But you can swim in the Thames in West London, from Putney Bridge and upstream. So, no swimming in the Thames in Central London and downstream.

Swimming in the Thames: the long answer

Long answer: deep breath… let’s dive in. (Sorry… couldn’t help myself.)

First, the good news: the Thames’ murky appearance is caused by the stirring of mud and silt from the riverbed due to the twice daily tides. In terms of water quality, it’s actually pretty clean and free from industrial waste. Believe it or not, it can support hundreds of plant species, and over 20 species of fresh water fish, including salmon. (Although maybe not in central London.)

But, here’s the bad news: even with all the progress that has been made with building an efficient sewer system, still too much raw sewage gets released into the river, especially after heavy rainfalls.

So there’s that.

What the law says about swimming in the Thames

And then there’s Bye law 21.1 from the Port of London Authority, the official body that regulates the tidal Thames (that’s the Thames in London and beyond, all the way out to the sea).

This bye law is very clear. Here it is in black and white:

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21. BATHING AND SWIMMING

21.1 A person must not without the prior permission of the PLA, given in writing, and in accordance with such conditions as the PLA may attach to any such permission:

a) swim (with or without a flotation device) in the Thames anywhere between Crossness and Putney Bridge, or;

b) bathe or swim in any fairway or designated anchorage, or where a notice is displayed by the PLA prohibiting bathing or swimming.

Why swimming in the Thames is really not a good idea

And they have plenty of good reasons for this bye law, all listed in very big letters on the Port of London Authority website. Among them?

• The river is bloody cold! As in freezing. Cold enough to cause sudden muscle weakness and trigger an involuntary gasp (a reflex that makes it hard to breathe when you’re suddenly submerged).

• The tides! Powerful enough to endanger even strong swimmers.

• The hidden currents! They can suck swimmers under in seconds.

• The sewage! Yeah, we talked about that already, but it bears repeating. The Thames is cleaner than it was in Victorian times (thank you, Sir Bazalgette) but still.

• The boats! Ferries, clippers, rowers, party boats, the odd lost paddleboarder, to name a few… The Thames is a working river. It carries over 20,000 ships every year. Ships can endanger swimmers, and swimmers can endanger ships. It’s the opposite of a mutually beneficial relationship…

Where swimming in the Thames is allowed

So the Port of London Authority only permits swimming in London between Putney Bridge and Teddington Lock.

Teddington Lock marks the boundary between the tidal and non-tidal Thames, and it’s where the PLA’s jurisdiction ends. Upstream of Teddington, the Thames is regulated by the Environment Agency.

And beyond Teddington Lock? Well, you’re still in London for a little while, and swimming IS permitted.

So there’s actually a sizeable stretch of the Thames you can swim in, if you really want to – the stretch from Putney Bridge to Teddington Lock is just under 18 kilometers. That’s over 300 swimming pool lengths, if you’re in the mood to do the whole thing in one go.

Most of the same caveats issued by the Port of London authority apply, though. Hidden currents, maritime traffic, sewage overflow…

You can swim in the River Thames in west London. Is it recommended? NO. Would you want to? Now that’s a question I’ll leave you to answer for yourself.

Looking for safer (and cleaner) places to swim? Here’s my full guide to open air swimming in London — nearly 20 spots across the city that don’t involve navigating sewage, tides or paddleboarders, from lidos to reservoirs. Two of them are even in central London!

The future of Thames swimming: floating pools in Central London?

And who knows — swimming in the Thames might one day be safer, cleaner, and actually enjoyable – even in central London. The Thames Baths Project is a plan by to bring safe outdoor swimming to central London, with floating pools filled with filtered river water. It’s still a proposal for now, but one that’s gained real momentum. So who knows… maybe that refreshing dip by the South Bank will one day be a reality?

So rather than going in the Thames, why not enjoy a delicious lunch next to it, at Comptoir Libanais in Kingston upon Thames, for example?