A high court in China's eastern Jiangsu province has fined six companies 160m yuan (£16.6m; $26m) for polluting rivers, state media report.
The Xinhua news agency said the fine was the highest ever in China as a result of public interest litigation against polluters.
The companies were found guilty in August of discharging 25,000 tonnes of chemical waste into two Taizhou rivers.
China's rapid economic growth has caused widespread environmental damage.
The country is facing international pressure to clean up its environment and an increasing number of local protests concerning pollution.
The government says that around 70% of China's lakes and rivers are polluted.
The BBC's Martin Patience in Beijing says the record fine will be welcomed by environmentalists as a sign that the government is finally prepared to get tough on polluters.
Taizhou Intermediate People's had already given jail terms to 14 people involved in the pollution but the companies, which have not been named, appealed against the fines, said Xinhua.
The Jiangsu Provincial Higher People's Court rejected the appeal and ordered the companies to pay the fines to an environmental protection fund within the next 30 days.