Most of wetland and scenery was destroyed later through rapid industrialization without environmental management. Polluting steel factories near the wetland simply dumped steel slag and other waste at the river bank, turning the riverbank into a refuse dump.

"Some piles of steel slag were more than 10 meters high; the dump nearly bordered the wetland," says Yang. "When it rained, the slag would flow into the river, making it dark and dirty. When the wind blew, the slag particles were caught in the air, making it choking."

And the many unemployed junkmen in the area also posed a threat to public security.

Therefore, the Baoshan District government decided in 2005 to clean up the area and revive the wetland. All the steel slag (the leftover from smelting ore) was buried deep. Soil, plants and trees were brought in and an ecological park was set up along the riverbank.

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]

"Unlike chemical discharges, steel slag won't damage the environment when it is buried deep," says Yang. "And the soil and plants above can help purify the water and soil."

Protecting what's left of the original wetland is a major task.