Swimming Ponds

It is a swimming body of water kept clean by biology instead of chemistry. A deep, unplanted swim zone is paired with a shallow gravel bed planted with reeds, rushes and iris, and a pump moves water slowly between them. Bacteria on the gravel and plant roots take up the nitrogen and phosphorus that algae would otherwise use, so the water stays clear without chlorine, bromine or salt. From a chair it reads as one pond, because the wall between the zones sits just below the surface. What you swim in is much closer to a clean lake than to a pool.

Yes, in a properly built and established pond. The regeneration zone removes the nutrient that would otherwise feed algae and bacteria, and continuous circulation and skimming handle the rest. Natural swimming pools have been standard across Europe for decades with a good public-health record, including at municipal scale. The water will not look like a chlorinated pool: expect a faint green cast, a living edge and a floor you can see rather than a tiled blue. If you want extra reassurance, an ultraviolet unit on the return is compatible with the system.

Some algae on rocks and on the gravel bed is normal and healthy, and it is part of what is doing the filtering. Green water is not, and it means the regeneration zone is undersized, the flow is short-circuiting through part of the bed instead of the whole of it, or the plants have not established yet. New ponds are cloudier in their first summer and improve markedly in the second as the roots and biofilm develop. Persistent green water in an established pond is a design problem rather than a treatment problem, which is why the bed sizing is the part we will not compromise on.

Often, yes, and it is a good use of an existing shell. The two routes are to build a regeneration zone alongside the pool and plumb the two together, keeping the full swim area, or to convert the shallow end of the existing shell into gravel and planting, which is cheaper and costs swim space. The existing structure, plumbing and equipment pad usually carry real value into the conversion. Conversions in Los Angeles typically run $40,000 to $90,000 depending on which route and how much of the existing hardware is reusable.

No, when they are running. Mosquitoes need still water for several days to complete a life cycle, and a swim pond circulates continuously with a skimmed surface. The regeneration zone also supports dragonfly larvae, damselflies and other predators that eat mosquito larvae, and fish can be added to the plant zone if you want more insurance. The Greater Los Angeles County Vector Control District provides mosquitofish to residents at no charge. The one real risk is a pond left with the pump off for a week in summer, which is true of any body of water.

Enough for the swim area you want plus a regeneration zone of a third to half the total water surface. In practice a usable swim pond starts around 800 to 1,000 square feet of total water, which needs a yard that can carry it plus the surround. This is why most of our swim pond work is on the larger lots out toward Calabasas, Hidden Hills, Tarzana, La Cañada and the bigger Palisades properties rather than on a standard city lot. If the space will not take a proper plant bed, we will say so rather than build something that goes green.

It tracks the weather, with no heater involved. In Los Angeles that means comfortable swimming from late spring through October in most years, and genuinely warm water in high summer because the shallow regeneration zone gains heat and feeds it back. It also means the pond is cold in January, unlike a heated pool. Some owners add solar heating to the swim zone, which works, though pushing water temperature much past the mid-eighties starts to affect the biology and is not something we encourage.

The work is gardening rather than chemistry. Skim the surface and keep the skimmer and pump clear, cut back and thin the regeneration planting once or twice a year, remove settled debris from the swim zone floor, top up for evaporation and check the flow distribution across the bed. There is nothing to test, no chlorine to dose, no salt cell to replace and no backwashing. Most owners find the hours comparable to a pool. We run seasonal visits for owners who would rather not do the plant work themselves.