Swimming ponds are a popular alternative to swimming pools because they cost about 20 percent of a real swimming pool and require about 20 percent of the maintenance work and ongoing costs. Another reason why swimming ponds are gaining some ground on backyard swimming ponds is because many people don't enjoy swimming in pool chemicals. Swimming ponds have flexible liners like a typical garden pond. Unlike swimming pools, swimming ponds let Mother Nature do the cleaning with aquatic plants that act as a skimmer or filter, or a small waterfall that provides pond aeration. Swimming ponds are regularly maintained with a UV sterilizer and a yearly vacuum of the pond's floor. A swimming pond can cost between $100 and $2000 online, depending on if you use a preformed pond, pond kit or customized pond design.