The opening of a dyke last Tuesday finally reconnected Baidang Lake in Anhui Province with the mighty Yangtze River.

A major freshwater initiative to restore the so-called "web of life" along the Yangzte River by linking up stranded lakes with the river's main flow is under way.

The reconnection program, part of the five-year eco-partnership between the World Wild Fund for Nature (WWF) and HSBC (Hongkong Shanghai Banking Corporation), started in 2002.

Zhangdu Lake, Honghu Lake and Tian'e-Zhou in Hubei, once known as the "Province of 1000 Lakes," are the scheme's pilot sites.

The Yangtze River is the world's third longest, with its basin covering an area three times larger than the United Kingdom. More than 100 lakes once dotted the area with natural channels linking the Yangtze's main tributaries. This system of interwoven streams and lakes creates a unique and complex ecosystem of rich biodiversity.

But river deltas are often the sites of heavy rainfall and extensive flooding. Farmers whose families have worked the rice paddies for generations are prone to contracting snail fever. The infection leads to the gradual destruction of the kidneys.

Snail fever is caused by blood flukes, which grow in lakes and rivers and swim into the paddies, according to Hu Huixin, a research fellow at the South China Research Institute for Endangered Species.

To prevent flooding and stop blood flukes from reaching rice paddies, dams and thousands of kilometers of dykes started to be built in the basin during the 1950s.

However, the dams and dykes often cut off water flow between rivers and lakes. Now only a few lakes, such as Poyang Lake and Dongting Lake, still have naturally occurring links with the Yangtze.

In recent years, environmentalists have begun to study the effect of damming on local biodiversity. They agree the Yangtze and its lakes once formed a complex wetland network providing just the right conditions for fish to spawn and feed.

But once they were disconnected, the natural flow of migratory fish was obstructed and biodiversity across the whole basin decreased dramatically.

"The dyke flood gates were built to prevent flooding and for irrigation, but no one considered the impact on water quality, fish migrating routes and flora and fauna," said Wang Limin, the restoration program manager.

According to Zhu Jiang, a program worker, the number of fish species found in Zhangdu Lake decreased to 40 from more than 90.

Following the construction of the dykes, intensive land reclamation has taken place, with both agricultural and urban settlements springing up on the former flood plains and around the lakes.

Baidang Lake has shrunk from 100 square kilometers in the 1950s to 40 square kilometers today. Zhangdu Lake has dwindled to one quarter of its original size. Lakes have also suffered from the inflow of farm run-off, and domestic and industrial sewage.

Deteriorating water quality has affected local ecology and wildlife. Natural fisheries output in the two lake regions has declined sharply.

Liao Guochao, a program worker, conducted a survey among local villagers around Zhangdu Lake.

Qiu Jinfa, in his 40s and from Qiuhu Village, told Liao the water quality in the lake was critical to fish production in his 2-hectare pond. To guarantee sufficient oxygen for the fish, Qiu would pipe in water regularly from the lake. Cleaner water could greatly reduce the risks of fish suffocating or contracting diseases.

"Without the natural water exchange with the river, the lake is quickly clogged with silt," said Zhu. The annual deposit of silt in Zhangdu Lake has increased from just one centimeter to an average depth of one meter.

"If the lake is kept isolated from the Yangtze River it will surely perish one day," said Zhu.

The environmentalists proposed seasonal opening of the dykes, off the flood season, to help restore the lakes' natural links to the Yangtze.

The seasonal opening coincides with the fish breeding season to enable the migratory flow of fish, allowing them to breed upstream in the Yangtze, and meaning young fish can try to return to the lake where they mature.

With water being piped from the lake, migratory fish can flow into surrounding ponds.

According to experts' estimates, reconnection of tributaries would allow local fisheries to increase yields by 5 per cent within the next three years.

Hu said the seasonal opening of the dykes taking environmental considerations into account will also help increase the variety of fish found in the lakes, helping the food chain to become better structured.

This action will also ensure a natural hydrological fluctuation in the lakes, allowing wetland areas to receive fresh water from the Yangtze, and subsequently thrive. This will ensure a healthy wetland ecosystem, according to Hu.

To prevent the re-entering of blood flukes during the linking period, the local governments now provide funds to build concrete snail-retention ponds between the first and second sluice gates linking the river and the lake.

Reducing pollution

The program workers have also been promoting the concept of environmentally-friendly farms and fisheries in the reconnection scheme, hoping to restore wetland habitats for displaced migratory and endemic birds, as well as reduce water pollution.

Local fish farmers have for a few years been using fertilizer. As a result, algae, which fish eat, grows and spreads quickly. But with the accumulation of poisonous substances in the fertilizer sinking into the silt, epidemics among fish have become increasingly frequent.

As fish catches declined year by year, Qiu Jinfa realized something was wrong with their farming methods.

So he joined an eco-fishery program advocated by the local government and the WWF, starting the more environmentally-friendly farming of species which feed on man-made fodder and demand a clean aquatic environment.

He is already reaping the economic benefits, making two to three times more than through traditional farming practices.

But it will take time to promote ecological farming among all villagers, according to Ye Qiusheng, a fisherman from Qihu Village.

But Liao Guochao is much more optimistic. "The local farmers are proud that more birds are inhabiting their regions. They know it is a sign of a better environment," he said.

(China Daily July 12, 2005)