Peng told Xinhua that the drones can provide video evidence and record the law enforcement process. "In this way, polluting firms fail to conceal their illegal behaviors," he said.

In addition to Foshan, China's Jilin province also uses UAVs to monitor the Mudanjiang River, a major waterway in northeast China, in a move to ensure water security.

East China's Zhejiang province uses UAVs to supervise factories and prevent them from stealthily pumping waste water into rivers or lakes.

UAVs bring a new trend to environmental protection. They also provide technical support in dealing with major environmental emergencies as well as assessment for construction projects, said Wang Qiao, an engineer with the Satellite Environment Center.

Wang said a new system, which could monitor the types, density and diffusion process of pollutants with the help of UAVs once emergencies happen, will be put into use soon.