Whitstable and Herne Bay were deliberately flooded with raw sewage by Southern Water to save money, a court has heard.
The sewage dumping took place between 2010 and 2015 in picturesque coastal areas including Whitstable, Herne Bay and the Solent, much of which has protected environmental status.
Andrew Marshall, representing the regulator, said the case was the “worst case brought by the Environment Agency in its history” and was brought about “by a deliberate lack of control and investment”.
The areas off the south coast of the UK are supposed to enjoy a high level of environmental protection due to their shellfish beds, which as a result of the pollution became contaminated with faecal bacteria.
The seas were flooded with raw sewage from storm tanks which the company allowed to be kept full and to turn septic instead of treating it as required by law, the court heard.
The case came about as a result of a five-year investigation, dubbed Operation Garden, launched following the deterioration of oyster beds and shellfish flesh.
In 2014 extremely high levels of faecal matter were found in the Swale, with the pollution stretching as far as Herne Bay.
In March last year the company pleaded guilty to 51 counts of dumping waste including raw sewage into the sea.
In a connected case, the company agreed to pay a record £126 million after an investigation by Ofwat, the economic regulator for the water industry, found that it had underinvested in its wastewater treatments works and deliberately misreported the performance of its sewage sites.
Rachel Fletcher, then-Ofwat chief executive, said at the time that the case was “shocking”.
“We have listened to all representations and think it is right to confirm the biggest package of penalties and rebates we’ve ever imposed,” she said.
A spokesperson for Southern Water said: “The charges relate to unpermitted discharges from 17 of our sites on the north Kent and Solent coasts. This hearing is for the judge to decide on the level of fine the company will pay as a sentence.”
The hearing continues. The water company is expected to make its representations and sentencing is due later this week.