The Pond in Your Park

Inspiration or Eyesore?

HAZELLE JACKSON reports from a seminar on Lake and Pond Management held in November at City Hall

Recent studies have shown that the problems facing the capital's lakes and ponds are far reaching and follow years of neglected maintenance over the last half century. We are now seeing the serious impact that decades of decline have had on the condition of lakes and ponds, on their amenity value to local communities and on the ecosystems they support. Yet a healthy pond is an attractive feature which adds greatly to the quality of a park and supports a wide range of wild life.

The restored lake in Peckham Rye Park

The restored lake in Peckham Rye Park
(Hazelle Jackson)

At a seminar in November on 'Biodiversity in London Lakes and Ponds', organised by the London Parks and Green Spaces Forum, the London Biodiversity Partnership, and the Mayor of London's Office, all the speakers emphasised that the solution to these problems involves many factors including managing water supply and quality, surrounding vegetation, access to the water for wildlife, management of fish and wildfowl stocks and even modifying public behaviour.

Valerie Selby, Principal Parks Officer (Biodiversity) for LB Wandsworth, who have shown the way in restoring park lakes in London, said it is vital parks managers start by asking some general questions, "Who uses our lakes?", "What for?" "What are the objectives for the lakes in future?".

Water Quality

Once these questions were addressed, it became possible to set some objectives and to explore more specific elements like the water supply, its quality and its source. Mains Water may be nutrient-rich and limited in supply. River water may bring with it undesirable debris and acquatic life. There may also be unidentified historic connections into the local pipe network.

Several delegates advocated the use of bore holes. These bring their own overheads, as they require negotiation with the water authority to install and annual licences and maintenance.

A major problem in many lakes and ponds is the silting up of the bottom. Several delegates lamented the near-obsession Londoners have with feeding ducks bags of mouldy bread. This sinks to the bottom and also sustains unhealthily large populations of waterfowl, which contribute further to the silt build-up.

If a large amount of silt has to be removed, this has to be tested for quality before it can be distributed safely. One popular solution is to line the edge of the lake with gabions (wire-covered packages of rock), then place coir rope coils in front and back fill with silt which is then planted. So far this does not seem to have caused major problems with nutrients running off into the water.

Debris and leaf mould have to be regularly collected and the lake inflows and outflows kept clear to keep the water healthy. A healthy supply of water needs adequate oxygen and this may require a pump or water feature like a bubbling fountain.

Birds and fish in a lake need regular monitoring and stocks may have to be reduced from time to time to keep them healthy. This can in turn agitate local wildlife lovers whose protests can be very time-consuming.

Canada Geese

Not all the wildlife in a lake is benign. One delegate asked about shooting Canada Geese as a means of pest control. Valerie Selby said this was not effective. Apart from removing the carcasses, if the geese were not breeding locally, another colony would move in. Pricking their eggs had proved the most effective method longer term.

Matthew Carter, the Environment Agency's Regional Fisheries Specialist, recommended a mix of roach, rudd, perch, trench, bream and some carp as a suitable mix of fish to stock a pond. He said that large numbers of carp can stir up the silt at the bottom of the pond, even though anglers like to catch them.

Terrapins, another menace (sometimes released into the lake by the public along with their goldfish!), are about as popular as Canada Geese, and can do as much damage to fish stocks as herons. They are extremely hard to catch.

Canada Geese were not the only intruders who needed tackling. Dogs swimming in lakes needed to be controlled and, when the public weren't feeding bread to the birds, they could often be found paddling in the lake in hot weather.

At the other end of the spectrum, park managers spent an inordinate amount of time with wildlife lovers who were opposed to any kind of cull or clearance programmes. Clearly a balance needs to be struck: dividing up a lake into different areas for different uses was being tried in several parks.

Dr Linda Barnett of Froglife talked about amphibians. In general frogs and toads do not co-exist well with wild fowl and fish. They need a more protected environment where they can co-exist with inveterbates, such as in smaller ponds.

Success Stories

There were success stories too. Rebecca Woodward of the Wildfowl and Wetlands Trust described work done to restore the lake at Brockwell Park. Ros Brewer of LB Tower Hamlets showed some impressive slides of the restoration of the East Lake in Victoria Park. And Jennifer O'Riley of the LB Kensington & Chelsea described their highly successful educational work with pond-dipping sessions for local schools in Holland Park.

Seminar Speakers:

The Green Menace

Ponds, lakes and watercourses are under assault from toxic blue-green algae and choking duckweed. MERVYN EDGECOMBE of Clearwater Pond and Lake Management Ltd says the problem is no idle threat.

A lot has been talked about the threat of climate change to many different aspects of our daily lives. However, nobody has yet pointed out the insidious - but seriously increasing -threat that a warmer climate poses to London's lakes, ponds, rivers and canal systems. Nature's two ugliest and potentially damaging aquatic mantles - highly toxic blue green algae and invasive duckweed - rampaged across every conceivable water area around the capital throughout July and August at almost Apocalyptic speeds. In some cases their green, choking pea soup-like masses achieved depths of over 1.5 metres in just a matter of days.

Once-picturesque water features enhancing the natural rhythms and undulations of our parks, historic houses and open spaces were turned, almost overnight, into unsightly, slimy eyesores not only distasteful to the eye but serious health hazards which, because of their de-oxygenised condition, were a fatal threat to every form of life within them from invertebrates and insects to aquatic flowers and fish.

Removing duckweed from Waterlow Park

Removing duckweed from Waterlow Park

Waterlow Park

One of our teams has just completed a major task for the London Borough of Camden at Waterlow Park, in Highgate, where we cleared three ponds and lakes of a serious infestation of Common Duckweed (Lemna minor), which had engulfed their entire areas to a depth of several inches in just weeks during the intense heat of summer. A staggering 12 tons of weed had to be removed to return them to a healthy condition.

For British Waterways, the duckweed and algae threats are even more extensive. Long stretches of the River Lee and the Limehouse Cut canal systems in London's East End were totally choked up by dense carpets over a metre in depth, created by the drought-like conditions of summer. And milder winters mean there is far less chance of the algae and duckweed being killed off by frost and cold conditions, as the organisms survive in water where the temperature does not drop below 9'C - heightening the gravity of the menace by the onset of Spring next year.

This scenario will be played out at every other pond, lake and watercourse - from private homes to large parks - which has been affected by both algae and common duckweed during this summer. Where water areas are relatively shallow and have little or no current, then the threat is greatest. Indeed, with heat - and, worse still, rich nutrient run- off into the water table - I would go so far as to say you have virtual laboratory-like growing conditions for the dreaded invaders to flourish.


Blue green algae - some people call it blanket weed - comes in two forms: the wispy filamentious type, often known as maidenhair, and the single cell species which creates the choking, pea soup-like carpets which reduce oxygen levels, leaving fish vulnerable to stress and suffocation and plant and aquatic life seriously endangered. It is so toxic that dogs which lick it could die in 30 minutes and scientists estimate that it comes somewhere between cobra venom and pufferfish in terms of how lethal it is.

Both forms are relatively simple organisms requiring very little encouragement to bloom and multiply asexually. Hot weather, plentiful sunshine and shallow, slow-moving water are the three key components for explosive growth. At the height of a hot summer like this year, the weed can easily grow up to six inches in depth in a fortnight.

What then is the answer?

Effective Control

Blue-green algae cannot be effectively controlled on an ad-hoc basis. But the algae can be controlled and very largely suppressed by all-year-round aquatic maintenance programmes. Anti-algae treatments, depending on the size of the water area(s) involved, need to be carried out between two or four times a year on a sustained on- going basis.

At the heart of the treatment programme is a material which is totally eco-friendly and readily available to anybody who knows a friendly farmer - barley straw. When this is immersed in the affected water, a 100% environmentally safe chemical reaction takes place with the algae which is then slowly and steadily destroyed and degraded by the straw. Usually, the first effects are visible within 2-3 weeks of the straw being submerged and its algae decomposing properties generally go on working for 2-4 months depending on the depth and density of the algae.

There is a technique as to how the barley straw should be deployed and how it is most effectively baled up for immersion. Similarly, at Clearwater we have developed a number of accelerants - all 100% enviro-friendly - which we mix in with the straw to carefully worked out levels and these speed up the decomposition process on the algae. This, in certain instances, can achieve quite startlingly rapid results.


With common duckweed the answer is manual, plain and simple. Operatives have to het into the water - wearing dry suits if necessary, and shift the clogging, suffocating mass from the water's surface by hand using booms and scoops.

It is dirty, exhausting hard labour and every microscopic leaf has to be removed if the threat of its return is to be eradicated. With the problem getting worse month by month because of no real cold winter weather any more, we are working flat-out to develop our own bespoke piece of equipment to make its removal a quicker and easier job.