Swimming can be great exercise and a lot of fun, not to mention an exciting sport at the Olympics. But the chlorine used in most pools can have some negative side effects, not the least of which is reliance on toxic (and finicky) chemicals.

Chlorine’s damaging effects on hair are well known, but few people realize that a number of studies have linked inhalation of the chemical by swimmers to increased asthma rates. A Norwegian study also documented an increased risk of wheezing among children who swim in pools before 6 months of age. In an unpleasant reaction, pee and sweat in water can react with chlorine to form toxic breakdown products known as chloramines.

[As astute reader Leslie has pointed out, the systems noted in the following paragraph, esp the ozone system, are not truly nontoxic, especially for canaries. It was an oversight on my part to include this paragraph; I was interested in promoting only the natural swimming pools as pictured. Thanks, Leslie!] For health, environmental and aesthetic reasons, a lot of people have expressed interest in alternatives to chlorine pools, and luckily there are more and more options to get wet without smelling like cleaning products. A company called TechnoPure offers alternative pool systems that treat water by pumping it through a chamber containing coated titanium plates and copper and zinc ions. The units cost a relatively affordable $5,500. DEL Ozone makes ozone injectors that can reduce the need for chlorine up to 90% — there’s been one installed at the White House for years! Some systems rely on a combination of ozone and copper and silver ions, while others are saline, though saltwater pools result in the formation of chlorine in the water.

One elegant, eco-friendly solution that has had enthusiastic supporters in Europe for decades is the so-called natural swimming pool, which is slowly beginning to gain buzz in the U.S. Natural swimming pools, often called swimming ponds across the Atlantic, can be beautiful oases of greenery and sustainability, as well as safe, fun places to take a dip.

Managed properly, natural swimming pools have crystal clear water and require no chemicals to maintain, as they are self-cleaning mini-ecosystems. “You can drink the water if you want to, and you don’t necessarily have to take a shower,” says Morgan Brown of Idaho-based Whole Water Systems, LLC. The natural pools designer says the systems also have lower maintenance costs than conventional pools, and their installation costs are not much more than standard designs.

Read on for more info on natural pools — sometimes called green pools or organic pools — and photos of some of the most gorgeous designs around.

Do it yourselfers can get help from Littlewood’s guide Natural Swimming Pools, A Guide for Building.

Natural landscape architect and garden designer Michael Littlewood of Somerset in the UK also has extensive experience in successfully designing natural swimming pools. In fact, he even wrote the first book in English on the subject, Natural Swimming Pools, Inspiration for Harmony with Nature, available on his website.