Chinese authorities have recovered about 100 tonnes (220,000lb) of poisoned fish from a river in central Hubei province, state media report.
The fish died after a chemical factory discharged ammonia into the Fuhe river, Xinhua news agency said.
Environmental officials blamed a nearby local firm for the incident.
This latest industrial incident comes after more than 16,000 dead pigs were recovered earlier this year from a river that runs through Shanghai.
China has faced increasing pollution problems as a result of decades of fast economic growth.