The river outside Putney will be empty tomorrow morning. From ten until half past two the Port of London Authority has closed the Thames to almost every boat between Brentford and Fulham, which takes in the whole of Putney’s frontage, the pier and the boathouses, so that several hundred people can swim down it.
You can watch from the Thames Path along the Embankment. Go late morning. The two official listings disagree about when the swim starts, but the closure notice does not, and the river is shut from ten until half two.
The 10km starts at Brentford and the 5km at Barnes, and both finish at Putney Embankment, where the organiser is putting up an event village with food, music and the prize-giving. Both swims are tide-assisted, which means the swimmers go downstream with the current doing much of the work, and they come down fast. The swimmers will move quickly enough that anyone following along the bank will need to keep up a brisk walk to stay level with them.
One thing worth knowing: a few hundred metres downstream of where the swimmers get out, swimming in the Thames is banned outright. The Port of London Authority permits it between Teddington Lock and Putney Bridge while saying it does not encourage it, and prohibits it below Putney Bridge, because the tide there runs at around five miles an hour and will beat the strongest swimmer. The finish at Putney Embankment sits on that line. The route stops where it does because that is where swimming stops being allowed.
What is actually happening on the water
The closure notice titles the event the Swim London 10K: Lords and Commons Cup. Nothing may navigate between Soaphouse Creek at Brentford and Fulham Railway Bridge for the four and a half hours. Boats working the event are exempt, and so are boats servicing Putney Pier, which have to call the PLA launch enforcing the closure on the radio and ask permission before they move.
The river reopens in stages as the swim moves downstream and passes Kew, Chiswick, Hammersmith Bridge, Craven Cottage and stretches of the Boat Race course on its way down.
Why anyone thinks this is a good idea
The event is built on the argument that the water has changed. The Thames Tideway Tunnel, the super sewer, was fully connected in February 2025 and is expected to stop about 95 per cent of the sewage that used to spill into the tidal river, cutting more than fifty discharges a year to roughly five.
That has not settled the argument about whether the river is becoming swimmable again. Thames Water, which is paying for the tunnel through customers’ bills, is still refusing to explain what killed the fish in Wimbledon Park Lake in July, citing a live pollution investigation.
Swim London was founded by Toby Robinson, who swam the 10km marathon for Britain at the Paris Olympics in 2024 and finished 14th. Before that he took part in a three-day relay swim down the Thames organised by Surfers Against Sewage, in protest at sewage discharges into the river. Swim London’s stated mission is a cleaner river.
If you are thinking of swimming it
Entry is open to anyone aged 18 or over. A tow float is compulsory, wetsuits are optional if the water is above 16C, and every swimmer wears a timing chip.
Swim London asks fees of £150 for the 10km and £130 for the 5km.
The organiser’s own terms say nobody should swim in the tidal Thames without the right experience, local knowledge and support on the water.
