The courts have been urged by a watchdog to issue tougher fines for environmental pollution.
The Environment Agency said bigger fines would send out a strong message to polluters that their behaviour would not be tolerated.
Its latest pollution statistics reveal that the number of cases of serious pollution in England and Wales dropped 13% from 827 in 2008 to 723 in 2007. This was down 44% from the 1,854 major incidents recorded in 2001, the Agency said.
The Environment Agency said its approach of targeting those whose activities have the highest environmental risks, or whose environmental track records are poor, has helped reduce the number of incidents of serious pollution.
Last year, it successfully brought 722 cases against companies and individuals for environmental offences, resulting in fines and costs of £5.3 million. The average fine against companies in 2008 was £10,080 - up from £8,229 the previous year.
The Environment Agency said this was encouraging evidence that the courts were recognising the growing seriousness of incidents.
Environment Agency chief executive, Dr Paul Leinster, said: "Major pollution incidents continue to reduce, thanks to more effective environmental regulation by the Environment Agency and efforts made by businesses to manage their activities better.
"We will continue to work with businesses and individuals to prevent incidents. But we will prosecute businesses and individuals where it is clear that they are not taking sufficient precautions.
"We want to see higher fines for pollution incidents to provide a greater deterrent.
"There are still an average of two serious pollution incidents a day and this is too many."
