Wu is not your typical environmentalist. In China, most activists are either urban professionals, working through nonprofit organizations, or university students. But Wu, 40, is a plainspoken farmer turned sound-equipment salesman who decided along the way that he couldn't tolerate the environmental devastation around him. When local authorities brushed off his complaints, he simply went over their heads and brought them to the attention of provincial officials. "This is a guy who is not afraid to let you know what he thinks," says Daniela Salaverry, who heads the China program at Pacific Environment, a California-based nonprofit that supports Wu's efforts. "He will get in your face." Wu has paid a price for his persistence: He lost his job, was severely beaten, and was regularly threatened by local officials long before his arrest. "We believe the charges brought against him are a result of his environmental advocacy work," says Salaverry. "Local authorities were concerned that he was making too much noise."

The central government has known about the Lake Tai pollution for years. With the rise of unregulated industry and large-scale farming over the last two decades, the lake has become seriously contaminated with nitrates and phosphates. Although Beijing spent millions of dollars trying to clean it up, hundreds of small private chemical factories are still operating along the banks, churning untreated wastewater into tributary rivers and the lake itself.

Angered by the blatant disregard for national regulations, Wu, whose village of Zhoutie is full of factories, became a one-man green movement. He would sneak around the lake, snapping photographs of pipes discharging chemicals—and then supply the pictures to local and foreign newspapers, to the provincial environmental protection agency, and to fellow activist Chen, who posted them on the Web site he had established. Wu was particularly outraged that, despite the pollution, which had turned the waters unearthly shades of blue and green, nearby Yixing, home to many chemical factories, had been selected by Beijing as an environmental model. To Wu the choice was a clear sign of dirty deals, and he planned to sue the national environmental protection agency in protest.

But Wu had made several enemies—from factory bosses exposed by his investigations to local officials who were angry about losing face. In 2003, he was beaten by thugs, and left with three broken ribs. "You'd better be careful, otherwise they're going to arrest you," Wu warned his friend, who had also been threatened.

"What am I afraid of?" replied Chen. "Let them arrest me. What great leader in the world hasn't spent time in jail?"

Wu had laughed in response. "You're a funny guy," he said.

But on April 13, it was Wu, not Chen, who was targeted. Some 20 police cars zoomed into his small village, blocking all exit points. According to Chinese press reports, more than 50 officers swarmed Wu's house and arrested him, leaving behind his wife and daughter. The timing—just a week before Wu planned to go to Beijing to sue the government—suggested political retaliation. And the drama surrounding the arrest seemed out of proportion to the alleged crime: Wu had allegedly extorted $2,000 from a factory boss in 2004 and about $5,000 from the village party secretary in 2006.