Video report by ITV News Meridian's Tony Green
Southern Water has been fined £90 million for deliberately dumping raw sewage into seas and rivers thousands of times.
The company admitted to 6,971 illegal spills between January 2010 and December 2015 across 17 sites in Kent, West Sussex and Hampshire.
Almost all of the sites were in protected, picturesque coastal areas.
The Environment Agency, who brought the landmark criminal case to court following its biggest ever investigation, claimed it was done deliberately for financial gain.
But defence lawyers for the firm insisted the 51 offences were committed due to "negligence".
However Mr Justice Jeremy Johnson disagreed and said: "I am satisfied so that I am sure that each of the offences were committed deliberately."
The judge initially fined Southern Water £135 million but reduced it by a third to £90 million due to the early guilty plea.
He slammed the "shocking and wholesale disregard to the environment" aggravated by "previous persistent pollution."
Southern Water, which has received 168 previous convictions and cautions, has been fined £2.7 million in three separate but similar cases since August 2013.
But Mr Johnson said "it had not learnt" and "it's offending simply continued".
The company's previous board of directors "flagrantly disregarded the law" by not investing in its "wholly inadequate" systems and instead making illegal discharges, the judge ruled.
Richard Matthews QC, defending, said Southern Water has undergone a "cultural change" and is "utterly committed from top to bottom to a transformation in transparency."
The Newton hearing, which began at Canterbury Crown Court, Kent on Tuesday, heard storm tanks were kept full and turned septic instead of being treated as required by law.
It heard each spill lasted about nine hours and in total sewage was spilt for 61,704 hours - just over seven years.
At some sites, wastewater was discharged at hundreds of litres per second with a total of 16 to 21 billion litres pumped into the sea, the equivalent of 7,400 Olympic swimming pools.
Southern Water admitted the charges during a previous hearing at Maidstone Crown Court, Kent in March last year.
They relate to the following sites:
Mr Matthews denied the company deliberately concealed spills and avoided telling the Environment Agency, represented during the hearing by Andrew Marshall.
Their five year investigation, dubbed Operation Garden, began when oyster beds in the River Swale were contaminated with E.coli, suggesting exposure to untreated sewage.
In a statement Southern Water's Chief Executive, Ian McAulay said:
"I am deeply sorry for the historic incidents which have led to today’s sentencing and fine. I know that the people who rely on us to be custodians of the precious environment in southern England must be able to trust us. What happened historically was completely unacceptable and Southern Water pleaded guilty to the charges in recognition of that fact.
"We have heard what the judge has said today and will reflect closely on the sentence and his remarks. He has rightly put the environment front and centre which is what matters to all of us.
"These events happened between 2010 and 2015. I joined Southern Water in 2017 and am passionately committed to the environment. We have changed the way we operate. My expectation is that Southern Water is fully transparent and operates in the right way. We continue to transform across the areas of risk and compliance, measurement and self-reporting. We have made much progress and are continuing to invest to protect the environment and deliver our services safely and at a fair price for our customers.
"Today’s fine will not impact customers’ bills and investment in our transformation will not be reduced. Our shareholders are bearing the cost of the fine."
Chair of the Environment Agency, Emma Howard Boyd said:
“With nature in crisis, no one should profit from undermining environmental laws. This sentence shows fines for environmental offences are starting to reach the same level as the highest fines for crimes in financial services and that is good.
"There is growing scrutiny of the environmental performance of companies all over the world, this sends an important message to global investors that England expects businesses to perform to the highest standards.
“Like all water companies, Southern Water has a responsibility to operate in accordance with permit conditions and protect against serious pollution. In its deliberate, widespread and repeated offending, it has failed the environment, customers and the system of environmental laws the public puts its trust in.
"Polluters must pay, the Environment Agency will continue to do everything in its power to ensure that they do.”
An Ofwat spokesperson said:
'Today’s sentencing serves as a timely reminder to Southern Water and the whole water sector about the importance of their responsibilities to their customers and the environment.
We will continue to push water companies to improve and protect the environment, leaving it in a better condition for generations to come, while providing the very best service for customers today.'