BEIJING - An environmental activist convicted on charges he blackmailed polluting businesses was sentenced to three years in prison on Friday after a seven-hour trial, his lawyer said.

Wu Lihong, named one of China's top 10 environmentalists in 2005, was arrested in April on what his wife and friends say were charges concocted by local officials who were embarrassed by Wu's whistle-blowing.

The court in the eastern city of Yixing also fined Wu $520 and ordered him to repay $5,900 that he allegedly extorted from the businesses, Zhu Xiaoyan, Wu's lawyer, told the Associated Press by phone.

"We will definitely appeal," Zhu said.

While China's communist leaders have called for stronger environmental protections, they remain wary of independent activists whose ranks have swelled in recent years alongside rising incomes and the spread of the Internet. The result, activists say, is a heightened friction and a strong disconnect between the government's aims and its often harsh treatment of whistle-blowers.

Wu's trial had initially been scheduled for June 12, but was postponed after lawyers requested a physical examination because they noticed marks on his arms. They said Wu told them he also suffered other injuries from beatings in police custody.

Wu, who has been collecting water samples from Lake Tai in eastern China for more than 15 years and reporting on its worsening condition, was arrested as he and a fellow activist were planning to travel to Beijing to present evidence of pollution to the central government.

According to the other activist, Chen Faqing, police warned Wu to end the campaign. On April 13, a week before he and Chen planned to present their case in Beijing, more than 50 officers raided Wu's home, carrying him away along with computers and files. Wu was charged with extorting $7,200 from businesses by threatening to expose polluters.

Throughout his years of advocacy, Wu faced repeated harassment and detention in Yixing. Three of his ribs were broken in a 2003 attack by thugs suspected of being sent by local authorities or factory owners.