Wu Lihong, an activist who crusaded for decades about the pollution of Lake Tai, the center of China’s ancient “land of fish and rice.” Mr. Wu, however, bore silent witness. Shortly before the algae crisis erupted in May, the authorities here in his hometown arrested him. In mid-August, with a fetid smell still wafting off the lake, a local court sentenced him to three years on an alchemy of charges that smacked of official retribution. Senior officials have tried to address environmental woes mostly through pulling the traditional levers of China’s authoritarian system: issuing command quotas on energy efficiency and emissions reduction; punishing corrupt officials who shield polluters; planting billions of trees across the country to hold back deserts and absorb carbon dioxide.

But they do not dare to unleash individuals who want to make China cleaner. Grass-roots environmentalists arguably do more to expose abuses than any edict emanating from Beijing. But they face a politica