Transgender women have been given full access to a women-only pond under a new policy.
Swimmers will be able to use ponds "aligning with their gender identity" on Hampstead Heath in north London.
The City of London Corporation's (CoLC) new rules said admission would be granted on a case-by-case basis.
Feminist campaigner Amy Desir, who uses Kenwood Ladies' Pond at Hampstead, called the policy "absolutely disgusting".
But writer and trans-commentator Jane Fae said she was "entirely unsurprised" by the CoLC policy.
She said: "All they have done is endorse the law as it stands. If they had done the opposite they would have been taken to court.
"The only people who appear to have broken the law are anti-trans protestors."
A consultation on attitudes to gender identity held last year received nearly 40,000 responses.
CoLC said 65% of the valid respondents to last year's survey favoured ensuring trans people did not suffer discrimination.
But 46% of the total responses to the consultation were disregarded as invalid on the basis that those respondents did not answer any questions, other than to identify themselves and declare the reason for their interest in the survey.
The gender identity policy also ensures transgender staff are not subject to "less favourable treatment" at work.
Ms Desir, from feminist campaign group ReSisters UK, said the policy "disproportionately discriminates against young women" and was "open to abuse".
She added: "Under the policy any man can self-identify and declare themselves a woman.
"The CoLC is deliberately misusing the Equalities Act and basing the policy on a biased survey."
Last year, female activists demonstrated against the right of trans women to use the women's pond by using the men's pond.
The Kenwood Ladies' Pond Association said it welcomed the decision.
A spokeswoman said: "The Ladies' Pond is a single sex space and the KLPA is committed to helping to create there an inclusive environment for all women, including transgender women, which is free from discrimination, harassment or victimisation.
"As we reflect on how we can provide a trans-friendly swimming environment, it is important to state that Kenwood Ladies' Pond Association welcomes to its membership transgender women."
Edward Lord, chair of the CoLC establishment committee, said: "This policy will ensure our public services do not discriminate against trans people.
"All communities should be fully respected, and equality and basic human rights upheld.
"We support a wide range of service users and we want to ensure they can all feel comfortable accessing and enjoying our facilities."