When you picture a backyard swimming pool, chances are you’re thinking of a concrete box, paved with tiles and filled with shimmering turquoise water that’s loaded with chlorine. And if you already have a traditional pool, you know that maintaining it is essentially a perpetual battle against nature: skimming out leaves, adding chemical cleansers, draining the pool in cold weather, refilling it in the spring.

But a new movement is changing the very concept of what a swimming pool is—and of what needs to be done to maintain it. For the first time, U.S. designers are looking to chemical-free, freshwater swimming pools that function a great deal like natural ponds, implementing the methods of water filtration that nature designed. These so-called natural swimming ponds are purified by water plants, which absorb impurities, as well as by other non-chemical means, like gravel filters and ultra-violet sterilizers.

After years of chlorine, we’ve only just come around to the idea that salt water pools are clean enough to swim in. So it almost takes a leap of faith to believe that a plant-filtration system could work. But the practice has actually been gaining traction in Europe for the past two decades.

“The concept is unfamiliar in the United States, but it’s starting to emerge on the West Coast,” says John McGlade, whose Gladwyne-based Bullfrog Ponds is one of the only firms on the East Coast to offer natural swimming ponds. In fact, McGlade just installed his first natural pool last year. But, he’s done two more since then—and, he says, it’s already apparent that the possibilities are endless.

He spent nearly six months researching the pools before installing his first one, but the basic principle is fairly simple. “It’s supported by an entirely natural approach to filtration and water management,” McGlade says. The essential elements are two sections of about equal size: first, the swimming area, which is clear of plants, and then, a water garden, which functions as a regeneration zone where plants like reeds and rushes absorb impurities. A drain beneath the regeneration area draws water through a bed of sand, gravel and roots—which also acts as a filter—to an external filtration system. In McGlade’s pools, water is then released into an ultraviolet sterilizer that kills off pathogens before being fed back into the swimming area.

“Unlike a chemical pool, which needs constant attention, the swimming pond will look after itself,” McGlade says. “It’s never going to be crystal clear like a pool, but you can see to the bottom of it.”

Jeffrey Rotwitt and his family were the first to request this service of McGlade; they already had a traditional pool, but began to consider the merits of a more natural pond. So McGlade created a 28,000-gallon natural swimming pond—complete with an island and three waterfalls—on the Rotwitts’ Radnor property. “It’s easier to maintain, and it’s certainly more aesthetic,” Rotwitt says. “When we want to dive and frolic and play volleyball we do it in the conventional pool, and when we want tranquility and aesthetic beauty, we go to our pond pool.” As for visitors to the pond, he says, “they’re smitten by it.”

And even though they function like ponds, these pools can take virtually any form.

Natural swimming ponds are always lined, either with rubber-like liners or with hard gunite shells, but the look can range from a natural appearance bordered by a water garden and with a beach entrance, to a sleek, formal swimming pool that is visually completely separate from the water garden or even fed by a waterfall from it. And if you like the idea of a natural purification system, but not the sight of it, the water garden could even be set some distance off from the pool itself. For one client, McGlade even created the atmosphere of a tropical beach, with pebbles underfoot and breezy cabanas nearby. It’s even possible (though not cheap) to retrofit an existing swimming pool to use as a natural swimming pond.

These pools start at around $25,000 and can run upwards of $60,000. In other words, they can cost just as much as a standard pool to install—but over time they require much less maintenance. In the winter, you don’t need to drain them; just change 10 percent to 15 percent of the water when you open the pool in the spring, making for a much more eco-friendly solution. They can be created at any size, although larger ponds are more stable, and they don’t attract mosquitoes because the water is circulating, not stagnant.

Sure, your pool may not look just like your neighbors’, but that’s only because you’ll be way ahead of the curve. If you’re thinking of installing a pool—but want a chemical-free experience—it just might be time to think outside the chlorinated turquoise box.