Like any mega engineering project, there are serious consequences and benefits to weigh up. The stakes don't get any higher than at the Three Gorges Dam, a topic that sharply divides environmentalists, scientists and the government. For years, Beijing has kept public dissent and discussion of the project under control. But a series of geological mishaps and an uncharacteristic warning of impending "environmental catastrophe" in the region reignited the controversy in a major way in 2007. News that another four million residents may be relocated - later explained as a "misunderstanding" - sparked even more unease. But the government moved qickly to douse criticisms of the project, with signs that a deeper and fuller reflection on the impact of the dam won't be conducted publicly for a while. [Visitors to the Three Gorges Dam view a model replica in an exhibition room. Sandouping, Nov 2007.]