The first hint that there is something unusual about the new outdoor swimming pool at Borden Park in Edmonton, Alberta, is what isn’t there—that insidious but telltale odor of chlorine. This is because the 64,000- square-foot recreational complex, which includes a sandy beach, changing rooms, and plenty of space to soak up the sun, is Canada’s first “natural” public swimming facility. Instead of using chlorine or other chemicals for disinfection, it relies on the cleansing capabilities of sand, gravel, and carefully selected aquatic plants and organisms.