London mayor Sir Sadiq Khan has been warned that his promise to create “swimmable rivers” in the capital by 2034 must not encourage people to swim in the dangerous tides of the Thames.

The mayor was re-elected last year on a manifesto which pledged he would “launch an ambitious plan to make rivers in London swimmable within 10 years”.

A senior official at the Port of London Authority (PLA), which manages the tidal section of the Thames, said the way in which the plan had been summarised in media headlines had caused concern.

A spokeswoman for Sir Sadiq said the tidal part of the Thames would never be safe to swim in but the mayor was committed to cleaning up areas where swimming would be safe.

Grace Rawnsley, the PLA’s director of sustainability, told City Hall’s environment committee: “I think when we get headlines like ‘swimmable Thames’, it does mean that people think that it’s safe to swim in.”

She added: “We’ve worked really hard over the last 15 years to reduce the number of deaths that we get in the Thames.

“Every year, people die by going into the water, in the tidal Thames…In 2023, I think there were 31 deaths in the tidal Thames, from people going in when they shouldn’t have gone in, or accidents, etc.

“In 2022, I believe 109 rescues happened in the tidal Thames, from people going in.

“So it’s about that knowledge, it’s about doing it in a safe way, and certainly in the tidal Thames we would always be discouraging that [swimming]… so it’s really important to have that kind of messaging about how you do that safely.”

The Thames is tidal for almost its entire course through London, only becoming non-tidal at Teddington Lock.

Between Teddington Lock and Putney Bridge, the PLA allows, but does not “encourage”, swimming, Ms Rawnsley said.

Any swimming in the Thames east of Putney Bridge is completely prohibited, as the PLA points out that, among other dangers, “powerful tides running at around five miles an hour will overpower even the strongest swimmers”.

A spokeswoman for Sir Sadiq said in response to Ms Rawnsley’s comments: “The Thames and its tributaries are the lifeblood of London, which the mayor is committed to cleaning up and protecting so that all Londoners can safely enjoy the benefits of nature – including swimming where safe to do so.

“The tidal part of the Thames will never be safe to swim in, but the Port of London Authority is responsible for ensuring this water is more generally safe and accessible to the public.”

Listen to the best of BBC Radio London on Sounds and follow BBC London on Facebook, X and Instagram. Send your story ideas to hello.bbclondon@bbc.co.uk