Swimmers' groups at Hampstead Ponds have hit out after bosses formally recommended doubling fees and enforcing payment.
Following a review, the City of London is recommending that charges for adult day tickets increase by 100 per cent to £4 this summer, with payment to be enforced by heath rangers.
At present swimmers are asked to pay £2 a visit, but it is not enforced.
The corporation says charging is needed because management costs have risen, as has demand for wild swimming.
But swimming groups have warned that “heavy-handed” enforcement plans were likely to lead to “chaos”.
Hampstead Heath management committee will decide what action to take on March 11.