Southern Water has been hit with a record £90 million fine for dumping colossal amounts of raw sewage into the sea for years.

The company unleashed up to 21 billion litres into protected waters - the equivalent of more than 700 Olympic swimming pools - with flagrant disregard to the law.

Southern was sentenced today at Canterbury Crown Court after admitting 6,971 illegal discharges from treatment works in Kent, West Sussex and Hampshire from 2010-2015.

While effluent destroyed whole oyster beds in the Swale and Solent rivers, with fishing businesses suffering, board members were aware of the huge scale of the illegal operation, the court heard.

The firm’s lawyers argued the sewage was discharged following “negligence” rather than a “deliberate” act to reap “considerable financial advantage”.

But employees would even go to “unprecedented” efforts to hinder the Environment Agency, as it sought to investigate the source of high levels of faecal matter, E coli and Norovirus.

Some 9,000-10,000 contaminated oysters are believed to have entered the food chain, dogs became violently ill after swimming, ships were damaged, and one home was almost flooded during a spill.

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His Honour Mr Justice Jeremy Johnson told Southern Water the evidence paints a “vivid and unsurprising picture” of its actions.

“Sanitary towels, condoms and tissues could be seen in the mooring lines of vessels, there was a strong smell of sewage, sewage was seen on the slipway, vessels had to be power-washed, ropes had to be replaced,” he explained.

“Dog walkers have been seen having to walk through sewage, there are reports of dogs becoming violently ill after swimming.

“Residents who live near the Swalecliffe site say the discharges were recurring events, they describe incidents where sewage has been seen flowing under the front gates of the site.

“A footbridge submerged, sewage flooding the road for 34 metres and pooling near a residents’ home.

“The footbridge is used by children going to and from school.”

“Sanitary towels, condoms and tissues could be seen in the mooring lines of vessels..."

The firm dumped sewage into The Swale affecting Sheppey, Whitstable and Herne Bay, where waters are protected to help maintain the ecosystem.

Raw sewage was also spilled into The Solent’s protected waters, between Southampton and Chichister.

Shellfish in both rivers were made unfit for human consumption and withdrawn from the market, but it is believed 9-10 thousand entered the human food chain, the court heards.

The Environment Agency launched Operation Garden, its biggest investigation to date, after high levels of E-coli were discovered in the Swale.

“On multiple occasions, employees would refuse to permit Environment Agency officers to take away documentation it wished to seize under statutory powers, refused them to walk around sites citing health and safety, and refused to answer questions despite the agency’s powers to require answers,” the judge continued.

Three employees, including a senior solicitor, were convicted for obstruction.

But the Environment Agency would later unearth evidence the firm systemically polluted the Swale, the Solent and Beaulieu River in the South Downs for 61,714 hours - the equivalent of seven years.

Mr Justice Jeremy Johnson said there was “an intentional breach of, and flagrant disregard for the law, by the board of directors.”

He told the court Southern has 168 convictions and cautions, adding it has “a wholesale disregard for the environment.”

It was fined 2 million in 2016 after untreated sewage polluted the sea and beach at Margate.

“The offences are aggravated by its previous persistent pollution of the environment over many years,” he continued.

Southern last year pleaded guilty to 51 counts of dumping poisonous, noxious substances including raw sewage between 2010-2015.

Water firms are allowed to occasionally release permitted levels of heavily diluted sewage during a storm to prevent overflow.

But Southern constantly opened storm tanks to release raw sewage in dry conditions, to save the cost of recycling, with proportions turning septic before entering the environment.

It is estimated the firm made £32m from its illegal activity.

Responding to the sentence, 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 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."

Kent sites:

Eastchurch, Isle of Sheppey

Swalecliffe, between Whitstable and Herne Bay

Queenborough, near Sheerness

Sittingbourne, Swale

Teynham, Swale

Herne Bay

Diamond Road, Whitstable

Hampshire sites:

Slowhill Copse

Budd’s Farm

Millbrook

Beaulieu

Ashlett Creek

Portswood in Southampton

Thornham

Woolston in Southampton

West Sussex:

Bosham

Chichester

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