When the Wenchuan earthquake killed some 80,000 people in southwest China in May of last year, suspicion immediately fell on the reservoir behind the nearby Zipingpu Dam. Seismologists knew that several hundred million tons of water had filled the reservoir in the preceding few years and that either the water itself or its weight might have weakened a nearby fault and unleashed the quake. A new analysis finds that both scenarios are plausible, but further insight will require the cooperation of the Chinese government. Last December, an American researcher was the first to prominently report (Science, 16 January, p. 322)...