Molars, mastodons, or plastic flowerpots?

For months, motorists cruising in and out of downtown Toronto have been wondering: What are six giant molars doing alongside the Don Valley Parkway? Or maybe they're supposed to be dinosaurs. Or truncated elephants...?

Now, it can be told. The baffling structures make up the Elevated Wetlands, a newly completed work of ecological public art. It combines form and beauty, or at least whimsy, with utility. The structures are part of a solar-powered water-filtration system to help purify the Don River. The plants in the structure, mostly indigenous, were chosen, in part, for their ability to neutralize toxins in the water.

Moreover, the Elevated Wetlands are an effort to demonstrate that plastic is a respectable medium for art. The Canadian Plastics Industry Association (CPIA) commissioned the acclaimed Toronto artist Noel Harding to create this work as the pilot project in its Plastics + Art initiative, intended to provide large-scale public art made out of plastic across Canada.

Most viewers, especially those going by at highway speed, will think the "molars" are concrete, but they are made of expanded polystyrene and coated with acrylic stucco for strength and weather resistance. The plants themselves are growing in a medium that includes plastics and recycled car parts. The water-filtration capacity of the wetlands is mostly symbolic, but CPIA president Pierre Dubois calls the work a "celebration of ecological process."

It will be used as the basis for an environmental unit in local public school curricula, too. The Elevated Wetlands took four years to research and develop, and although artist Harding calls it "a very simple work," its construction was a complex public-works project involving earthmovers, as well as 200 volunteers who helped plant greenery around the site. "I'm not the kind of artist who can carve things myself," Mr. Harding said at the recent celebration of the completion of the work.

"It's nice to see the arts not separated from the sciences," he added, noting that the solar-powered water pumps used to bring water from the Don up into the tubs were originally developed for use in the third world. The pumps work only when the sun is shining on them. Breaks in the flow of water are good for the plants. "When it's dark, the roots aerate and harden," Harding explained, as his grandson toddled among the elephantine legs of the sculpture.

"It's a beautiful, whimsical thing you come upon on the parkway," said Toronto City Councilor Howard Moscow. "I haven't met anyone who hasn't liked it."