Fish in more than 6.7 square-km waters, including a 4 square-km lake, had become extinct after fish farmers poisoned the water with pesticides in east China's Anhui Province, local authorities said Wednesday.

Pan Jinbiao and other fish farmers, who planned to grow water plant gordong euryale seed in the 4 square-km Luojia Lake, dumped 560 kilograms of pesticide Fenvalerate on April 9 to exterminate the lake's fish in Baizehu Township of Anqing City, said a spokesman with the municipal fishery authority.

The poisoning had posed great threat to the nearby 22.7-square-km Pogang Lake. More than 3 square-km of Pogang Lake had been polluted, the spokesman said.

Workers with the fishery authorities are trying to block the poisonous water from polluting nearby waters but the pollution is expanding. They are also carrying dead fish to be buried or burned, he added.

Such an amount of pesticide can pollute 33-square-km of waters, the spokesman said.

The fishery authority has reported the case to the police for further investigation.

Fenvalerate can cause damage to human nervous system and takes nearly 20 days to be biodegraded.