Zipping past Taylor Creek Park on the Don Valley Parkway, there's something large and animal-like among the trees at the side of the road. It's a little like a herd of elephants, something like a bunch of crooked molars, but before long it's gone from the rear view mirror.

The strange shapes - six of them in total - are actually functional sculptures by Canadian artist Noel Harding. For more than 16 years, Elevated Wetlands (the installation's proper title) has intrigued drivers and park goers while providing an important service to the surrounding ecosystem.

Commissioned by the Canadian Plastics Industry Association, "the voice of the Canadian Plastics Industry," the solar-powered devices draw water up from the Don River and filter it through layers of recycled plastic and automobile fluff, removing pollutants. Wetland trees are planted in the artificial soil and hydrated by the flow of water, boosting the hydroponic process.

The CPIA and City of Toronto split the $1 million cost of building the acrylic-coated polystyrene shapes in 1997 and the first batch of shrubs, trees, and plants was planted by volunteers the same year. 4,000 more arrived in 1998 in the hands of volunteers. Plastics + Art Limited Partnership, the original owner of the partly city-financed shapes, donated the work to Toronto in 2004.

In all, the little ecosystem comprises grassland and a cluster of small ponds that act as a way station for the clean water before it re-enters the river. Where there was once dry salt bed there is now lush plant life.

Although most public interaction with Elevated Wetlands happens within the confines of a car, the shapes are accessible on foot from the west end of the Taylor Creek Trail. Auto access is off Don Mills Road just north of the DVP cloverleaf.

The enigmatic essence of the grey shapes was intentional, the artist told the Toronto Star in 2005. "I wanted it to have meanings, not a meaning," Harding said. "I was after a kind of aura, intrigue. The question: 'What's that' is more interesting than the answer."

Chris Bateman is a staff writer at blogTO. Follow him on Twitter at @chrisbateman.

Image: Bad Alley/Flickr Creative Commons