It is hard to imagine that people can still find a natural oasis in Shanghai.
But amid the steel and cement forest, where nearly every inch of land is covered with high buildings and large mansions, Jiangwan marshland proves there are areas that have not been encroached.
To many locals the northeastern Yangpu District area is still known as "Jiangwan Airport" - where the Chinese People's Liberation Army once had an air base. No military aircraft have landed in the area for about 10 years.
Built in 1922, Jiangwan Airport was the first military airport in China. For many years it was a forbidden sector for civilians.
The name "Jiangwan" came from the airport's unique geographic location. It is close to the first bend of the Huangpu River.
The marshland is about two kilometers from Wujiaochang in northeast Shanghai, a main traffic artery, and covers more than eight square kilometers.
Although it is surrounded by row-upon-row of newly built residential buildings, the marshland remains pristine and is regarded as the last natural landscape in Shanghai.
The Yangtze River and the East China Sea are only a few kilometers away.
Because of its rich water resources and the lack of human disturbance, the area evolved into a complete ecological network and heaven for wild life.
Reed marshes measuring more than two meters are found stretching off into the horizon. From time to time one or two unnamed birds send out a cry and pass by quickly in the sky.
It is said that more than 280 wild plant species and nearly 40 freshwater plants accumulate in the Jiangwan marshland.
Ornithologists, those who study birds, have discovered about 36 species, many rarely seen. They account for 88 percent of summer birds in the city.
Apart from its significance to scientific research, the large wetland known as the city's "green lung" has also contributed to improving the environment.
It was also once a good place for locals to relax during weekends and holidays. But those days are gone.
More and more bird catchers, fisherman and farmers flocked to the area. To protect Jiangwan marshland, the area was enclosed by tall walls and people are forbidden to enter the area.
"It is a pity that we are not allowed to enter the wetland anymore," said Liu Yi, a biology teacher from a nearby high school. "Once I took my students there to explore the land's purity. Unfortunately, we were stopped at the entrance."
According to Liu, about four years ago when she was still a university student, she started paying close attention to the Wujiaochang area and the wetland.
The biology teacher said at the time, she and many of her teachers and schoolmates entered the "beautiful secret land" and left with many interesting discoveries.
"Since I live close to the Jiangwan Airport, I have the chance to witness all the changes that have happened to the land these years," Liu said.
"Although we are not allowed to enter anymore, I always talk to my students about the importance of protecting such a place in Shanghai."
Liu calls for more attention and protection to the marshland, both from the government and ordinary people.
To build itself into one of the country's garden cities and upgrade its image as an international metropolis, Shanghai is sparing no effort to develop large areas of green space downtown.
Inch by inch, green space in Shanghai is growing.
According to the Shanghai Landscape Administration Bureau, there was more than seven square meters of green space per capita at the end of last year. Greenery covers more than 28 percent of the city.
Downtown, people can find a large public park of more than 3,000 square meters within walking distance.
However, to set up artificial green space requires a huge investment and serious labor - trees are transplanted from other provinces.
It is said that one square meter of green space in an urban area costs 10,000 yuan (US$1,200). This figure was cited after Yanzhong Greenland was built since many residents were relocated and trees were transplanted to the area.
People started asking that if it costs so much to create greenery, why not pay more attention to existing ecological resources such as Jiangwan?
After all, large-scale public parks have few plants species and are unable to form a real ecosystem such as Jiangwan marshland, experts said.