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Water levels in Wanstead Park


The City of London Corporation own four lakes at Wanstead Park. These lakes along with one owned by our neighbours comprise a five-lake cascade that formed the centrepiece in one of England’s most significant gardens.

For much of the lake system’s history water supply has been a persistent problem with many episodes of low water levels. For the last few years low water levels at two of the lakes, Heronry Pond and Ornamental Waters, have been a developing concern. In 2017 substantial works were completed that have helped reduce these problems, including the daily pumping of 345,600 litres of water into the lakes. This summer’s drought conditions have however exacerbated the long-standing water management problems of the lake system.

We are doing everything possible to maintain water levels at Wanstead Park during this challenging heatwave. In the longer term the Registered Park’s four landowners, Historic England and the Friends of Wanstead parklands are working on a plan that will address water conservation within the 300 year-old lake system; the safety of the dams and the Park’s Grade II* Heritage Landscape. This will be a significant and costly initiative and would represent a historic development for the Park. However, given the ambitious nature of this change, it will take some years to come to fruition.

Below is an update on the current situation.

Water management

Long-term concerns

Water supply

Detailed hydrological assessments undertaken by specialist engineers have shown that there is insufficient natural water to keep the lakes filled. Water losses from leakage and evaporation outstrip the amount of water entering the lakes and if we did not pump water into the lakes they would ultimately be much reduced in size, if not lost.

The water being pumped into the lakes is good quality drinking water. We have been advised that increasing pressure for drinking water in London could lead to increased restrictions on our ability to pump water into the lakes. This would lead to even further water management problems for the lake system as less water would be available to keep the lakes filled. Finding a solution to this issue is an important longer-term management challenge that underlies much of the Parks future development proposals.

Large Raised Reservoirs

Three of the four City of London managed lakes are classed as Large Raised Reservoirs (LRR). Under the requirements of the Flood and Water Management Act 2010 the Environment Agency undertook in 2014 a risk-based review of LRR and have recently confirmed they have upgraded the Risk Category of the lakes at Wanstead Park to High Risk.

The implications of the upgraded risk category on the lakes and their associated infrastructure are still being evaluated by specialist engineers. It is anticipated that significant modifications will be required to some of the dams on the lakes to ensure they comply with the Reservoir Act requirements.

Recent successes

In 2017 we successfully resolved two important problems that were causing water management problems.

Borehole pump replacement

Following the breakdown of the pump used to abstract water from the borehole to keep the lakes filled, a new pump was installed in 2017. The pump is situated 88m below ground and cost £35,000 to replace. Since installation the pump has been working on two eight-hour pumping cycles a day with water going directly into either the Perch Pond on the Heronry Pond.

Floating pennywort

Over the last few years as part of a £13,000 project we have sought to control the spread of Floating Pennywort. In 2016 specialist contractors manually removed around 40 tonnes of weed from the Perch Pond and undertook a monthly herbicide treatment of remaining colonies of the weed. Earlier than we expected by a couple of years our contractors have managed to reduce the floating pennywort to a level where we were able once again allow water to flow from the Perch Pond to Ornamental Waters in the Autumn of 2017. As a result we were able to commence restoration of the water levels in the Ornamental Waters following a few years when the risk of the floating pennywort spreading prevented us from doing so.

Current problems

Ornamental Waters

Following the installation of the new pump and the recommencement of pumping water into the Ornamental Waters water levels rose to ensure the lake bed was completely covered. Water levels however stopped rising at a point around 75cm below what we expected them to rise to.

The Ornamental Water is located on very porous river bed sediments and does not hold water well. In addition, it is possible that leakage problems have been exacerbated by the historic installation of water and gas services close to and under the Ornamental Water. At around 7 acres in extent securing the water holding ability through reducing leakage from the Ornamental Water is a considerable technical and financial problem.

We anticipate that once the current drought conditions subside we will be able to restore water levels in the Ornamental Water to the improved levels we obtained in the Spring of 2018. This still leaves us with the longer-term problem of identifying a means of restoring water levels to the full lake capacity and this is something that will need to form part of larger longer-term hydrological improvements being worked on for Wanstead Park as a whole

Drought conditions

The Environment Agency reports that we have experienced one of the driest Junes since records began and July is likely to have been equally dry. Consistently high temperatures and a lengthy lack of rainfall are contributing to falling water levels in lakes and ponds across England, including Wanstead Park. The River Roding is currently classed as having notably low river and ground water levels. Current weather conditions are unfortunately exacerbating an already difficult situation with regard to Ornamental Water, however, in contrast, to recent years we have been able to maintain the Heronry Pond to relatively normal levels.

Fish welfare

High temperatures and reduced water levels can lead to difficult conditions for fish in the lakes. On Friday 10th August low oxygen levels in the Perch Pond led to staff installing pumps to aerate the lake. Specialist contractors were subsequently called in to help with aerating the lake and happily dissolved oxygen levels were restored to normal levels. The same contractors also assessed the welfare of the fish and no further immediate actions were thought necessary. Regular monitoring by staff will inform what further actions will be required as the situation develops.

A longer-term improvement we are aware of is the possible installation of permanent aerators in the Perch Pond, which has a history of poor aeration, and remedying this forms part of longer term plans.

Blue green algae

We have recently observed a possible Blue Green Algae bloom in the Perch Pond. The Environment Agency have been informed and are undertaking tests to confirm if we have Blue Green Algae present

Blue-green algae naturally occur in inland waters, estuaries and the sea – and they are important contributors to the biology of fresh and marine waters. But where high levels of phosphorus combine with other factors such as increased sunlight and temperature, the numbers of blue-green algae can rapidly increase. Blue Green Algal blooms can have a temporary negative effect on the appearance, quality and use of the water. They can produce toxins which can harm and be potentially fatal for wild animals, farm livestock and pets. Algal blooms are however a natural process and we need to allow time for the algae at the lake to clear on its own.

Precautionary signs have been placed at the site warning people against fishing, swimming or letting animals in the water while managers monitor the situation with the Environment Agency. Blue-green algae has so far not been identified at any of the other lakes in the park, however, the City of London Corporation is monitoring the sites and advising visitors not to enter them.

If you come into contact with blue-green algae, seek medical advice if you have any health effects. If pets come in contact with the water, wash them thoroughly with fresh water and dry them to prevent them grooming themselves and ingesting any potential algae. If you are concerned, take your dog to a vet.


The improvements of 2017 have ensured that we have been better able to respond to the difficult weather conditions of this summer with levels in the Heronry Pond maintained at relatively normal capacity.

However, it has undeniably been another difficult year for the Ornamental Water and its condition is a source of distress to us all. There are however no easy fixes to the problems at Ornamental Water and they also form part of a wider package of hydrological works required, including potentially significant legally required works to the dams.

We are however optimistic that once the drought conditions end we can return the Ornamental Water to an improved position over the winter months.

23 March 2017
Last Modified:
23 August 2018