• Jean-Marc Daigle

Natural Swimming Pools: A Freshwater Alternative

Updated: Apr 30, 2018

Jean-Marc Daigle


I love nothing more than a long refreshing swim on a hot summer day in a cool, clear lake, and then hanging out on a warm slab of shoreline rock to dry off and soak it all in. Growing up in northern Quebec, water was a big part of my youth and to this day, I still look forward with unbridled enthusiasm to those rare moments when I can escape the city and head north to Georgian Bay or a Muskoka lake for a freshwater dip.

I’ve never been much of a swimming pool aficionado. Sure, I might still dive in with boyish excitement, but enthusiasm is inevitably dampened by the dizzying smell of chlorine, burning eyes and irritated skin. Inevitably, I always end up pining for a jump in a lake.

That's why I was immediately drawn to the idea of Natural Swimming Pools (NSP) when I first heard about them, and why I have become such an advocate. They are immensely popular across Europe and Great Britain, and its been my mission over the last 12 years to advance the concept here in Ontario.

That's me, enjoying a swim in one of our Natural Swimming Pools
That's Me, Swimming Among the Frogs and Lily Pads

Genus Loci (www.genus-loci.ca) built its first one in 2006, and since then, we have built over a dozen of them. NSP's still represent only a tiny fraction of the swimming pool market, but I do believe they are on an upward trend. Other landscape companies such as Ayr, ON based Quiet Nature Inc. are now building and promoting NSP's, and this growth will help propel the concept forward.

So, if you are like most people, you are probably wondering what exactly is an NSP?

In a nutshell, an NSP's is a freshwater, chemical-free alternative to the conventional chlorinated pool. Conventional pools rely on chlorine and other chemical sterilizers to keep the water clear and clean and devoid of any life form (other than swimmers). NSP’s, on the other hand, are anything but sterile. In fact, they are designed to promote aquatic life rather than eliminate it, relying on a combination of plants, biological filters and mechanical filtration systems to keep the water clean, clear and fresh.

Like conventional pool, NSP's are built on high ground and are completely lined and sealed, relying on pumps and an elaborate circulation system to move and purify water several times a day through the mechanical and aquatic plant filters. It may seem counter-intuitive, but NSP's should not be constructed in wet, low-lying areas that are subject to nutrient loading from both ground water and surface run-off, as this will render the system ineffective. We regularly field calls from landowners with existing ponds or wet low-lying areas who are disappointed to learn that their site is in fact not suited to an NSP.

I intend to touch on this subject in more detail in future blogs.

NSP’s can be designed to suit any style and aesthetic preference. Most of the ones we have built are decidedly natural and organic in appearance, but they can also be shaped and design to a more contemporary modern aesthetic.

Regardless of the aesthetics, there are a few basic design constants.

First, the pool basin is carefully sculpted with a wide perimeter shelf and a central deep zone, and then lined with a durable heavy-duty EPDM or PVC liner. The key feature of the pond design is a submerged retaining wall that separates the swim zone from the plant filters. The retaining wall is backfilled with graded granite rock and peastone, with serves both as a biomedia for beneficial bacteria, as well as a growing medium for the aquatic plants. Limestone should not be used in this application, as it reacts with the water and can alter its pH to the detriment of the aquatic plants.

A wide range of native aquatic plant species are introduced into the pool, setting roots into the porous peastone. Aquatic plants are the NSP's signature element, taking centre stage both in terms of visual appeal and biological filtration.

The NSP includes a pump-driven circulation system specifically designed to circulate the water through the plant filters, through perforated pipes placed under the stone. The pool is then inoculated with beneficial aerobic bacteria, which colonizes the granite stone and biofilters. Once established, the bacteria will break down organic debris into element nutruients, which in turn are drawn out of the water by the aquatic plants, effectively starving out algae.

Genus Loci NSP's typically also include a back-up biological filter, either in the form of a "biofall" or a pressure filter, to maximize the bacterial action in the pool. Every pool includes a waterfall, to agitate and oxygenate the water, and to serve as a centrepiece. Mechanical skimmers and ionizers are also included in the system to ensure continuous high level filtration, and we typically recommend the installation of a UV filter to eliminate with potential pathogens.

Designs can also include diving docks or rock slab, accent boulders, steps, and underwater lighting, and the surrounding landscape can be accessorized much like any other pool. What I really appreciate about the pond format is that you don’t have to swim in it to enjoy the benefits. An artfully created NSP can be a strikingly beautiful landscape feature. And in the winter, the pond can make a great skating surface, since you do not have to lower the water levels in the fall.

Yes, there are “bugs” in the system - literally. Within a few days of filling a natural swimming pool, water boatmen and water striders will make an appearance, along with a coterie of other harmless – and in fact beneficial – creatures, such as butterflies, dragonflies, frogs, newts and songbirds. This, in fact, is the integral beauty of NSP's: not only are they are great to swim in and visually striking in all seasons, they also create wonderfully diverse aquatic habitat teeming with life.

Granted, NSP’s are not for everyone.

The squeamish among us may shudder at the thought of swimming next to plants and other aquatic creatures, and some may be put off by the slippery biofilm - where the beneficial bacteria reside - that adorns the pool surfaces.

Nor are NSP’s suited to every site. Natural pond designs generally require more space than a conventional pool to accommodate the plant filters, and are better suited to larger properties (though pools can be sized for smaller lots).

Contrary to popular misconceptions, NSP’s are not hands-off and maintenance-free. The requirements are certainly no more onerous than those associated with a conventional pool, but must not be ignored.

Price-wise, NSP’s tend to be on par with custom designed concrete pools (roughly around $125 - $130/ft2 of swim zone), and cannot compete with lower fibreglass or vinyl pools.

These drawbacks aside, NSP’s are an ideal swimming solution for the motivated client on the right property, offering a beautiful, refreshing, ecologically sensible alternative to the conventional pool. So, if the idea of freshwater swimming turns you on, then I say “go jump in a lake - in your own backyard!”

For more information on Natural Swimming Pools, go to: https://www.genus-loci.ca/natural-swimming-ponds, and you can see numerous examples of our pools at https://www.genus-loci.ca/natural-swimming-ponds-gallery

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