Activist Wu Lihong was arrested in April on trumped-up extortion charges and has since suffered beatings while in custody, Xu Jiehua told AFP by phone from her home in Yixing city on the west side of the lake.

"My husband has been tortured... the police whipped him on his back, arms, legs and feet," Xu said, adding his lawyer had seen bruises on Wu during a jail visit on Wednesday.

The 39-year-old environmental campaigner was arrested as he was preparing a lawsuit against the local government for allowing Taihu, China's third biggest freshwater lake, to become polluted.

Xu insisted her husband had been set up and that he was not guilty of extortion or bribery as alleged. No trial date has been set.

"His work offended the local authorities so they set a trap for him. They wanted to silence him," she said.

Wu has fought for years against the pollution of Taihu lake in the centre of the Yangtze River Delta plain, a region known for its natural beauty but now littered with light industry and chemical factories.

This week a massive algae bloom in the lake contaminated drinking supplies for millions of people in Wuxi city on the northeastern side, sparking panic buying of bottled water.