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Technical blog - natural swimming pools

— 04 Aug 2020 by David Bridges

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Natural swimming pools offer the benefits of a traditional outdoor pool but with the features of a large garden pond or lake that make them so inviting for swimming in a natural environment.

Natural swimming pools establish an organic micro-eco-system which regulates the health and clarity of the water without resorting to chemical treatment.

Non-geometric shapes lend themselves to the ethos of natural pools. The shape can be excavated and simply finished with shingle over a pond liner (for the most natural appearance) or a bespoke reinforced concrete shell can be formed using sprayed concrete on a steel framework with a dividing wall between the pool area and the filter bed.

The filter bed will become a natural habitat for frogs, newts, dragonflies, reeds, grasses and flowering water plants; just like a pond or lake so selection of local flora to complement the pool is encouraged.

How it works

The key with a natural pool is to keep a balanced eco-system with a low level of nutrients. Zooplankton (microscopic animals) are extremely efficient at eating and eliminating Phytoplankton (microscopic plants, including algae) and bacteria. Under normal circumstances in nature the Zooplankton population can deal with the Phytoplankton and bacteria populations, and the result is clear and healthy water.

The micro-organisms are assisted in keeping the water clean with the aggregate filter bed of special shingle. The efficacy can be further boosted with a pump that draws the water through the filter medium and back into the water body, keeping the level of phosphates to a minimum to discourage blanket weed growth. The aggregate typically requires replacement every 15 years.

A heat exchanger can be included as part of the circulation pipework to boost the temperature and extend the season for outdoor swimming or just to ensure the summer months have consistent water temperatures.


  • No chemical (no smell of chlorine or red eyes)
  • More sympathetic to informal curtilage gardens as a natural water feature rather than a swimming pool.
  • Provides a habitat for local flora and fauna
  • Exciting organic designs
  • Can be heated


  • Still requires maintenance (little and often) to remove leaves and organic debris
  • Size of swimming area is controlled by volume of filter bed required. Therefore, an equivalent sized traditional swimming pool would require less space overall.

Please contact us for more information on natural swimming pools, or to discuss your project.

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