The extensive hydropower development in the upper reaches of the Yangtze River will threaten the safety of Shanghai's water supply in the future, an expert with the World Wildlife Fund (WWF) said Thursday.

"One of the most direct consequences for Shanghai is the reduction of the total amount of fresh water that flows from the upper reaches," said Yong Yi, a project manager from the WWF's Shanghai office. "This will cause water safety problems for Shanghai, because the coastal city will suffer from seawater intrusion."

Areas in the Yangtze's lower reaches have already experienced changes, including longer droughts and shorter flood seasons, Yong said. Still, the changes are difficult for the average person to perceive.

The WWF released a scientific report on the upper reaches of the Yangtze River based on a 12-day scientific investigation of the entire Jinsha River Basin in June, the Shanghai Evening Post reported.

The Jinsha River is one of the major headwaters of the Yangtze River. It runs through three provinces before converging with another river in Sichuan Province to form the Yangtze.

The scientists found that more than 25 hydropower stations have been planned along the river, more than half of which were already under development.

The construction of the hydropower stations has tamed the Jinsha, once a rapid and tumultuous river that carried silt down to the Yangtze's lower reaches, Yong said.

"The sand and soil are very important for Shanghai, which sits on the tip of the alluvial plain of the Yangtze River Delta," Yong told the Global Times. "With the Yangtze River carrying down less sand and soil, the tidal flat will shrink. The flat is considered an important land reserve."

The intensive hydropower development has also had a destructive impact on the ecosystem along the Yangtze. During their expedition, scientists found 17 species of fish in the Jinsha River, down from 143 species in the past.

The situation has been aggravated by overfishing, which brought some species to the brink of extinction. "The problem we have found is that the more fishermen fish, the poorer they become," Zhao Yimin, director of the executive office of the Yangtze Fishery Resources Commission of the Ministry of Agriculture.

Experts and scientists have called for a moratorium on fishing along the Yangtze River to allow the ecosystem to rebuild itself. However, any ban would face many obstacles, including finding new ways for fishermen to support themselves.