The City of London Corporation, which runs Hampstead Heath, offers guidance for swimming at the open-air bathing ponds.

People wishing to swim on Hampstead Heath should only use one of three designated bathing areas and only within opening hours. These are the Ladies’, Mixed and Men’s ponds.

These facilities have qualified lifeguards and are safe areas to swim in.

The water is deep, cold and muddy and visitors should only enter if they are strong swimmers, the City advises.

The City urges swimmers not to swim in any of the unsupervised ponds as they have uneven banks, varying depths and hazards such as reeds, weeds and sharp objects on the bottom.

Before swimming in the ponds, the City advises that visitors should make sure they are physically fit to do so. If in doubt, they should consult their GP.

If visitors are swimming for the first time on the Heath, it is advisable to speak with a lifeguard before entering the water.

The City reminds visitors that even strong swimmers can get into trouble in the water.

If a swimmer feels tired or unwell, they should get out of the water immediately and if necessary notify a lifeguard.

The water temperature of the ponds is currently 12C.

The City offers cold water swimming guidelines for when water drops below this temperature.

They advise that swimmers should be used to swimming in cold water and habituate by entering the water regularly for short periods of time.

In a statement, a City spokesman said that water safety is given paramount importance by Heath staff.

All ponds are supervised by teams of highly trained lifeguards, trained to Royal Life Saving Society Standard.

Each lifeguard attends regular training sessions throughout the year.