Women's rights campaigners stormed Hampstead Heath's male-only pond on Bank Holiday Monday, wearing false beards, wigs and moustaches in protest.
Around 30 women demanded entry to the male bathing area, claiming they self-identified as men.
The demonstration was organised after the City of London Corporation, which manages the Heath's ponds, ruled that transgender women could continue using the ladies-only pond.
Security guards and police blocked their entry, locking a gate while insisting that protests were not permitted on the premises.
The women were seen holding placards saying 'let women swim'
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The women were protesting following a Supreme Court ruling that the legal definition of a woman should be based on biological sex.
Protesters waved placards stating "let women swim" and "no peens in our pond" as they marched towards the male bathing area.
The group loudly sang: "The law says no. Men must go. No goolies in our poolies. If the person has a penis, he's a man."
Visitors to the pond looked on bemused as the demonstration unfolded on what protesters dubbed "Bank Holiday Man-Day".
Hannah Clarke, who jumped into the male pond, said: "The Supreme Court has made the definition of a woman categorically clear, and that's somebody who is born a woman.
"The City of London Corporation should be complying with the law; it's as simple as that."
The protesters swam for approximately 20 minutes in the male-only pond.
They then jumped in the air and waved to supporters while standing on a wooden platform overlooking the pond.
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Around 30 women joined the protest
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The City of London Corporation has stated it is "carefully considering the judgement" while awaiting statutory guidance from the Commission.
A spokesman for the Corporation told the media: "These accusations are completely false.
"The City Corporation is compliant with existing UK law."
The male-only pond is one of three bathing ponds at Hampstead Heath, alongside the ladies' pond and a mixed-gender swimming area.
