Zijin Mining, China's largest gold producer, will investigate its management methods after wastewater from a mine contaminated a river in Fujian province.
Zijin spokesman Zhao Jugang said the accident reflects deep issues within the company and that the closure of the plant and an investigation are necessary.
Wastewater containing acidic copper leaked from the mine on 3 July, contaminating the Ting River.
About 1.89 million kilograms of fish in the province's Mianhuatan reservoir were found dead.
Zijin has been criticised for only disclosing the accident to its investors nine days after it took place.