"The 50-hectare wetland is a precious treasure for the ecosystem here," says Yang. He calls wetland "the kidney of Earth," a purifier and filter that protects water resources.

Paotaiwan (Emplacement) Wetland Park in Shanghai's northern Baoshan District, an ecological paradise, was built three years ago where vast heaps of steel slag and junk were encroaching. [Shanghai Daily]

Ecologists call wetlands transitional areas between terrestrial ecosystems and aquatic systems; the two systems are inherently different from each other, yet dependent on each other. They meet in the wetlands that are places of great biodiversity. Many water birds only reproduce in wetlands.

Wetland, forest and ocean are considered the three great ecosystems.

Wetland not only provides a friendly habitat for many creatures but also protects water resources on the land. Polluting substances in water will naturally precipitate when a river or stream flows slowly through a wetland; toxins will break down while nutrients will nourish plants.

Wetlands can help prevent drought and flood through its exchange between underground water and surface runoff. They also can prevent seawater from invading the land and freshwater.

Yet the "kidney of Earth" couldn't possibly purify the many tons of refuse along the river in Baoshan District. No water birds or migratory birds would ever nest where the water was dark and smelly and the air was suffocating.

"Luckily, with our efforts, we have successfully turned the dump back into an ecological area," says Yang. "Water plants like wild water bamboo are found again here and many birds have discovered this wonderful habitat. You will find seagulls there these days."

The park was opened to the public in May 2007. Because of the damage that too many visitors can cause, officials decided to charge 5-yuan admission to discourage too many sightseers. The original plan had called for free admission.

It took about 150 million yuan (US$22 million) to move the refuse piles and build the first phase of the park, according to Yang. Another 300 million yuan will be spent to complete Phase II of an additional 20 hectares.

"We plan to complete an ecological zone along the riverbank in time for World Expo 2010 opening in May 2010," says Yang.

Opening hours: 5am-5pm (free during 5-7am)

Address: 206 Tanghou Rd, Wusong, Baoshan District

Admission: 5 yuan

Tel: 5657-9007