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The Hampstead Ponds or Highgate Ponds are three large freshwater swimming ponds — two designated single sex, and one for mixed bathing — fed by the headwater springs of the River Fleet, in Hampstead Heath, North London, England. The swimming ponds are three out of some 30 ponds on Hampstead Heath. They were originally dug in the 17th and 18th centuries as reservoirs. A malarial marsh was drained by the Hampstead Water Company in 1777 to meet London's growing water demand.
In 2004, the City of London Corporation, which holds the Heath in trust since the abolition of the Greater London Council in 1986, tried to close the ponds on the grounds that they were an unsustainable drain on their expenses and posed a health risk to swimmers. The swimmers challenged this and won a victory in the High Court. To defray costs, the Corporation introduced a charge for admission of £2 per session, £1 for concessions. There was some opposition to this on the grounds that swimming there had been free since at least the 1920s, and some ticket machines were vandalised.
Hampstead has three different ponds for swimming: one for men, one for women and one mixed. Only swimmers over eight years of age are allowed; those between eight and 15 years old must be in the care of an adult. Winter swimming is sometimes available at the ponds, which remain popular with users.
The men's pond had a diving tower, but this was dismantled following an accident in the 1970s and only a low level board remains, along with showers and a small sunbathing and changing area.
Quality of water tests — which comply with EU regulations — are routinely performed on all three swimming ponds, and results are available through the official City of London website. The three ponds are not to be confused with Parliament Hill Lido, built in 1938, now with a stainless steel lining.
Proposals for the ponds and dams
It was announced in 2011 that the City of London was proposing extensive works on the ponds and dams, which it claimed were necessary for safety reasons in the event of a rare major storm. The proposals included measures to improve the water quality of the ponds as well as improvements to the pipes and weirs that allow water to cascade from one pond to the other. These initial recommendations followed engineers' reports in 2005 that the hydrology of the ponds was poorly understood. These same engineering reports resulted in engineering works in 2006 on the two ponds in the grounds of Kenwood House, to make their overflow structures and dams safer. Since 2011 there has been strong opposition from the swimming clubs and the Protect Our Ponds campaign. In 2013 a united campaign was launched called Dam Nonsense to oppose the works, which the campaign says is unnecessary and in conflict with the Hampstead Heath Act 1871. The campaign includes all the groups opposed to the proposals. The proposed work on the Hampstead Heath dams is further complicated by the regulations embodied in the 1975 Reservoir Act, which only relate to three dams on the Heath, and the proposed regulations under the Flood and Water Management Act 2010 which potentially relate to all 14 dams on the Heath. The Heath and Hampstead Society took the engineering decisions of the City of London to judicial review in November 2014: the interpretation of the 1975 Reservoir Act was challenged and thereby the nature of the proposed engineering works to the dams. The case was heard by The Honourable Mrs Justice Lang (DBE) and a ruling, in favour of the City of London, was issued on 28 November 2014 (case number CO/4175/2014). The judgement also addressed the status of the proposed engineering works relative to the provisions of the 1871 Act, again ruling that the engineers had shown due consideration for the provisions of the Act. Following the judicial review, the City of London now awaits the decision on the planning application for the engineering works, which is being opposed by The Heath and Hampstead Society and the Dam Nonsense campaign.
If the work goes ahead it is likely to involve the closure of all three swimming ponds for a prolonged period of time to enable higher dams to be built which will raise their heights, in the case of the dam above the Men's Swimming Pond by 18 feet. The City of London Corporation has said the work should be carried out urgently to reduce danger of flooding in surrounding built-up residential areas in the event of one of the dams bursting. The initial estimate of the number of lives which might be lost, in the event of a dam collapse in an extreme flood event, was over 2000  (2006 estimate). This figure has been reduced to less than 400, still a large number. However the chance of such an event is one in 400,000 years. At a public meeting to launch the Dam Nonsense Campaign held on 25 November 2013, more than 200 people voted in favour of the campaign with only one vote against.
The regulated dams under the 1975 Reservoir Act are the Model Pond and the Men's Bathing Pond in the Highgate Chain. Highgate Number 1 pond would have been covered by the Act but the water level was lowered by the GLC in 1984. In the Hampstead chain, Hampstead Number 1 pond is also regulated under the 1975 Act.
The men's and women's ponds are on the eastern side of the park, off Millfield Lane. The mixed bathing pond is in the centre of the Heath, and is a 10-15 minute walk from Hampstead Heath railway station and from South End Green, at the junction of Pond Street and East Heath Road, which is served by several bus routes.
- Ponds and dams, City of London Corporation.
- Protect Our Ponds documents the debate since 2011 until the present time[when?] regarding the proposed works to the dams on the Heath ponds, including the three swimming ponds.
- The London Encyclopaedia, Ben Weinreb and Christopher Hibbert, Macmillan.
-  Highgate Men's Pond Association (HMPA) is an organisation of swimmers set up in 2012. It has a chair, secretary and treasurer plus a committee of 12, all democratically elected. It currently (Dec 2013) has 550 supporters on email list, many of whom pay an annual subscription.
- Protect Our Ponds
- The London Encyclopaedia, Ben Weinreb and Christopher Hibbert, Macmillan.* City of London Corporation, Swimming on Hampstead Heath, also gives water temperatures.
- Diving at Highgate Ponds on the Lost Lidos website.