The ‘natural’ swimming pools cleansed by plants, not chemicals
We’ll send you a myFT Daily Digest email rounding up the latest Life & Arts news every morning.
On a chilly day in June, I had my first swim in a natural (man-made) swimming pond. Shaped like a kidney, outlined in what felt like hazard tape, King’s Cross Pond Club in north London is surrounded by a construction site, yet the water is pristine, purified naturally by aquatic plants: spiked water milfoil, water lily and galingale, to name a few.
While tough pioneers such as toadflax, wild thistle and purple loosestrife establish themselves on the soil along the border, the vegetation in this London pond varies according to depth. Water milfoil, Canadian pondweed and white waterlily are typical of deeper water, while common rush and yellow flag iris are characteristic of the margins. The plant-filter zone and regeneration area are where the plants do their work, separated by a barrier beneath the water surface to keep them from tangling with bathers in the swimming section. Submerged oxygenators absorb and transform superfluous nutrients into whorls of mare’s tail and patches of lily pads, while marsh marigold and monkey musk make their bed by a smoky mattress of Norfolk reed. Poking out from the water, reed stems act like snorkels, taking oxygen from the air and releasing it back into the water through their roots.
Fresh water with no chemical disinfectants is good for swimmers’ skin, and attracts a host of acrobatic insects. Old-world creatures such as damselfly feed on mosquito larvae, using leggy stems of flag iris to emerge from the water for their flirtatious flight. Flicking metallic wings wink at others: pond skaters, water boatmen and iridescent dragonfly. Surprisingly for their size, many aquatic species depend on freshwater ponds for refuge, including more than 100 UK Biodiversity Action Plan priority species. Despite the building work, swimming chemical-free at King’s Cross Pond Club feels very natural. If only there were more.
Indeed, the tide may well be turning against chlorine, with 20,000 man-made chemical-free pools in Europe, and their popularity gaining in the US. The + POOL is a crowdfunded pool conceived by designers Family and PlayLab for the Hudson river. It will filter 600,000 gallons of polluted New York river water every day without chemicals. Another freshwater swimming option in London could materialise with Studio Octopi’s Thames Baths Project, which proposes using reed beds, rushes and salt marsh flora as filters for its floating pontoon near Victoria Embankment. Protected areas of planting ranging from saline plants such as sea beet and sea aster to freshwater species including yellow flag iris would mimic the stages of succession from salt marsh to freshwater wetland.
Rather than utilitarian landscapes behind chain fences, where cattails and tussock sedge are put to work for waste management or flood control, projects such as this employ wetland plants for pleasure. Getting to know them by swimming, we understand their value in terms of wellbeing and are more likely to want to protect them.
Garden ponds and swimming ponds are becoming increasingly important for wildlife, as the habitats on which they rely are lost due to intense farming and water pollution. According to the Freshwater Habitats Trust, 80 per cent of UK ponds are in very poor condition. By making a freshwater swimming pond, you are supporting an ecosystem.
“Natural swimming ponds are a very good haven for aquatic plants, and the more diverse they are the better they work,” says Jonathan Newman, an aquatic botanist at the UK-based Centre for Ecology and Hydrology, who would like to see many more of his favourite native species, such as opposite-leaved pondweed (Groenlandia densa) in swimming ponds.
Planting schemes are devised by expert pool builders using a combination of submerged and emergent species that lean heavily on vigorous natives to lift nutrients from the water quickly. Identified by their green stems and bright flowers, plants such as marsh marigold, water mint and brandy bottle work hard so that swimming ponds require little maintenance. Foliage will need cutting back in autumn, the same as a conventional pool or garden pond or — if you prefer — most contractors offer a maintenance service to meet your needs.
Biotop, which has been providing natural swimming pools around the world for the past 30 years, was behind the King’s Cross Pond Club. One of the 5,000 or so natural pools it has helped create is in Istanbul and covers 12,000 sq metres. With almost no size limit, a natural swimming pond costs from €300 to €600 per sq metre and the price decreases as the area of the swimming pond increases. Designs are landscaped to site — and individual — requirements, so construction costs may be high compared with traditional pools. Over time, however, natural pond owners save on the cost of chemicals and expensive filtration equipment.
As well as their ecological benefits, swimming ponds are strikingly pretty and give gardeners a chance to discover a whole new world of spectacular water plants. Inside the Grand Pavilion at Chelsea Flower Show this year, Linda Smith of Waterside Nursery stood by her aquatic fantasia.
The same trusty reliables that clean the waters at King’s Cross were there, decorated in gold, along with more flamboyant varieties such as Iris sibirica Sparkling Rose. Cotton-wool heads of Eriophorum angustifoliums softened the tall spiky umbels of sedge, while arrow-leaved Sagittaria sagittifolia, pointed to miniature water gardens around the main pond: 60cm to 80cm puddles for sun or shade-loving plants.
The EU Water Framework Directive says ponds must measure at least one sq metre. So officially, these aren’t ponds. But for the aquatic universe, every small swimming pond makes a big splash.
What are reputed to be the oldest swimming pools in western Europe recently secured more than £366,000 from the Heritage Lottery Fund for refurbishment, writes Claudia Knowles. Cleveland Pools in Bath, in the west of England, date back 200 years, when an advert was placed in the Bath Chronicle asking for subscriptions “to provide a place in connection with the River, where those who swim and those who do not will be alike accommodated”. It took two years to gather money for what is one of the first examples of “subscription pools”, funded by private money for public use.
The site’s popularity was fuelled by the Bathwick Water Act of 1801, which prohibited nude river bathing, depriving locals of their daily dip (Georgian garb tended to be too cumbersome for a fully clothed swim). The result was a crescent-shaped diversion of the nearby river Avon, with a spring-fed ladies’ plunge pool and perpetual shower installed in 1827. The Grade II*-listed Georgian pools prospered in the Victorian era, and a children’s pool was added in 1861.
In 1984 the pools fell silent and closed when funding was rerouted to the city’s new sports and leisure centre. No bathers have splashed around on the surface since, but that is about to change.
In addition to the lottery grant, Cleveland Pools Trust has gathered funding from the local council and private donations, and has almost reached its £4.27m target. The facility could reopen for year-round swimming by spring 2018.
Photographs: John Sturrock; James Veysey; Gillian Plummer/Gap Photos; Jonathan Buckley/Gap; Marg Cousens/Gap Photos; Fiona Lea/Gap Photos; Bath Records Office
Get alerts on Life & Arts when a new story is published