Is China's Three Gorges Dam to blame for the devastating drought last spring in the downstream reaches of the Yangtze River?

Popular opinion, including several Chinese scientists, government officials, and the press have said yes, some even arguing that drought on the Yangtze will become chronic thanks to the dam.

Now, the Chinese Academy of Social Sciences, an agency affiliated with China's State Council, has entered the debate, arguing that there is no scientific evidence that Three Gorges caused changes to the climate or is to blame for meteorological disasters in recent years.

This debate, one of the hottest inside China, has become politically explosive because it goes to the heart of whether the Three Gorges Dam should have been built, and whether heads should roll in the Chinese leadership.

The dam, the world's largest hydropower project, faced blistering criticism this past spring when it was blamed for aggravating China's worst drought in 50 years -- by storing water upstream that was needed for purposes of power generation, it deprived areas downstream. As a result, critics say, China's two largest freshwater lakes, Poyang and Dongting, all but vanished, fish stocks died off and shipping on the Yangtze -- China's most important water transportation route -- was suspended

Eventually, the dam's operators were forced to release water to relieve the downstream areas. Suspicions grew that authorities had not properly anticipated the downstream costs of damming the Three Gorges.

They should have, according to Fan Xiao, Chief Engineer with the Sichuan Geology and Mineral Bureau, who says this year's drought was nothing new. The annual filling of the Three Gorges dam reservoir has reduced water levels downstream in the Yangtze basin and caused a plethora of problems for the millions of people who live and work along the banks of the Yangtze River.

In 2006, just after the reservoir level was raised to 156 metres above sea level for the first time, water levels downstream at Dongting Lake plummeted to the lowest levels in history, exposing much of the lake bottom. This caused an infestation of rats, destruction of fish habitats, and saltwater intrusion of seawater into the estuary at Shanghai, which threatened the city's water supply.

Then in October 2009, when dam operators tried to fill the reservoir to its maximum height of 175 metres, water levels in the middle and lower reaches of the Yangtze dropped precipitously and ships ran aground. The dam operators were ordered to release water and their attempt to fill the reservoir was aborted.

Then in 2010, Three Gorges' officials were under pressure to show that the dam could generate power at full throttle so they tried again to fill the reservoir. This time they succeeded, but at the highest price to date.

As Three Gorges' reservoir filled with the largest amount of water ever, China's worst drought in 50 years hit and scenes of dead fish, exposed riverbed and beached ships downstream began showing up in newspapers around the world.

China's cabinet, the State Council, was forced to admit that the Three Gorges Dam had "problems... which should be solved urgently," but did not concede that the dam had caused or exacerbated the drought conditions. The Yangtze River Water Resources Committee, a government agency that manages the river, even took credit, bizarrely, for relieving the downstream drought conditions by releasing water.

Now, China's Academy of Social Sciences has come to the defence of Three Gorges -- and the government -- by claiming that "extreme weather conditions," not the dam, caused the drought. None of this washes with the millions living downstream who know that their water shortages began when the Three Gorges reservoir began to fill and that this year's drop in precipitation was a mere aggravation of what has become a man-made problem -- chronic water shortages caused by the damming of the Yangtze.

Patricia Adams is the Executive Director of Probe International, a Toronto-based environmental organization. She is also the editor of the English translation of "Yangtze! Yangtze!" and "The River Dragon has Come!"