In an interview published by Oriental Weekly on Dec. 17, Cao Wenxuan, an academician at the Chinese Academy of Sciences, warned about the potential impact of the south-to-north water diversion project on local fish species and the entire ecosystem.

An academician at the Chinese Academy of Sciences warned about the potential impact of the south-to-north water diversion project on local fish species and the entire ecosystem.

Cao first mentioned the Hanjiang, the largest tributary of the Yangtze River. Its source is in Hanzhong, in west China's Shaanxi Province, and it is reputed for having the best water quality in China. It is the main supply source for the middle of the three proposed diversion channels.

"One third of the water in the upper reaches of the Hanjiang will be transferred to the northern parts of the country," said Cao.

This will result in a sharp decrease in the volume of water at the river's source. In dry seasons, water from the Tangbai River, the largest tributary of the Hanjiang, actually flows backward to replenish the mainstream. However, this results in lower mainstream water quality, because its tributary is severely polluted.

In addition, many fish have adapted to the swift river flows. With more and more reservoirs and dams being built, the flow of the rivers has slowed down. The silt that is deposited raises the level of the riverbed each year, causing water levels to drop, Cao said. The reservoirs and dams that block the flow between rivers and lakes also destroy the supply of minute aquatic creatures on which fish feed.

More than 120 fish species in the upper reaches of the Yangtze River have suffered. "This is the main reason why the number of fish in the Yangtze River has dropped dramatically over the past few years. "

As planned, terraced water conservancy works will be extended to Xiangfan, central China's Hubei Province where Poyang Lake, China's second largest freshwater lake, is located.

The lake has been subject to prolonged dry seasons throughout the last decade due to reduced water supply from the Yangtze River and low precipitation in Jiangxi. Last month, the surface area was only 293 square kilometers, substantially less than in the wet season, according to Xinhua. This has made drinking water scarce, crippled the local fishing industry and threatened the lake's ecology.

Poyang Lake was once teeming with rare fish. For example, the largest group of black finless porpoises lived there. However, there were only 450 recorded in 2010, and the figure is expected to continue to decrease if the water level falls in the future, said Cao.

He also cited the example of the East Lake in Wuhan, Hubei Province. "Since graduating from university in 1955, I have worked at the Institute of Hydrobiology of the Chinese Academy of Sciences for 58 years, during which time I have witnessed the changes of the East Lake."

"In the early 1960s, there were as many as 83 kinds of aquatic creatures in the lake. The number dropped to 52 in the early 1990s and 14 in 2013." At the same time, he said, the number of fish species dropped from 79 in the 1960s to less than 20 currently.

"Many wild ducks and water birds used to fly to the East Lake for winter. Such scenes are rare now, as there are few fish for them now, and less grass," Cao said.

"To regain the vigor of the lake, the most important thing is to restore the relationship between the lake and rivers - the seasonal rising and falling of water levels. In addition, waste water discharged from local enterprises must be discharged through pipelines and must not be discharged into the lake untreated", he suggested.

Local governments increased protection of the ecosystem in the water diversion project in recent years. "While building water storage projects, they have paid attention to the protection of wetlands where flocks of water fowl live. It will also help black finless porpoises to survive."

Speaking of the ecosystem in the upper reaches of the Yangtze River, Cao said it faces more threats from the water diversion project. "The ecosystem in the upper reaches of the Yangtze River is more fragile. Production and the lives of the local people will be impacted, so the problem can't be neglected."

The south-to-north water diversion project has become China's largest water conservation project since the completion of the Three Gorges Dam in August 2009, Cao said. It is a strategic infrastructure project to alleviate serious water shortages in north China.

The project will draw water from the Yangtze River through three channels - the east, the middle and the west - to supply 44.8 billion cubic meters of water. By last March, cumulative investment in the project exceeded 223.4 billion yuan (about US$36.8 billion).