Its 2022 Water Quality Report uncovers "potential illegal" sewage discharges alongside more than 700 cases of illness that are attributed to the releases.
The report used rainfall data to investigate potentially illegal "dry spills" – sewage outflows are typically only permitted in unusually heavy rainfall when infrastructure is unable to cope.
Southern Water was responsible for four times as many dry spills as the next worst offender, South West Water, SAS said.
The analysis also shows that some water companies offloaded untreated sewage into waterways even when there hasn't been any rain. This summer, SAS claimed that there were 5,504 incidences of raw sewage being dumped into bathing waters over a period collectively lasting for longer than 15,000 hours.
The untreated sewage contaminated beaches and riverbanks which water enthusiasts, holidaymakers and families used for recreational activities throughout the summer.
The report also found 103 times where sewage overflows occurred at bathing waters across England yet the firms responsible failed to report their activity for a period of more than two weeks during the bathing season. Some 44 sewage overflows were found to have been left completely unmonitored throughout the entire season.
Water company CEOs were paid a total of £16.5m in the last financial year, whilst shareholders received a total of £965m despite all but one water company making a loss this year.
"Shareholders and CEOs are unashamedly profiteering off pollution. And the government is complicit in the sewage scandal, failing to enforce and strengthen regulations to protect the health of the UK's waterways – and the health of its citizens," said Amy Slack, head of campaigns and policy at SAS.
"Politicians are simply kicking the can down the road, legitimising sewage pollution for the next 27 years, through the sewage action plan published this summer."
Elsewhere in the report, some 400 accounts of sickness from people swimming and surfing in bathing waters were identified.
Some 720 sickness reports were received in total, from water-users who got ill after going in the water in the last year, with more than 70 per cent of them suffering from symptoms of gastroenteritis, including persistent diarrhoea and vomiting.
Some of the worst cases of sickness included Leptospirosis and kidney failure.
Two-thirds of cases who saw their doctor had their sickness attributed to contaminated water exposure, and many reported stays in hospital. A third of reports were directly linked to a sewage spill.
A Southern Water spokesman said: "Storm releases, which go a long way to reduce the impact of the type of flooding we have seen recently, and which are permitted by the Environmental Agency, reduced by nearly 50 per cent this year compared to last, in part due to a dry summer.
"We're investing £2bn to improve environmental performance and further reduce their use by increasing storage capacity and working with partners to reduce the rain run-off entering the system."
A Defra spokesperson said: "Our storm overflows discharge reduction plan has brought in strict targets on sewage pollution and will require water companies to deliver the largest infrastructure programme in their history to tackle storm sewage discharges – a £56bn capital investment over 25 years.
"We have been clear that water companies cannot profit from environmental damage. Through increased monitoring and transparency, driven by government, the regulators have launched the largest criminal and civil investigations into water company sewage treatment works ever.
"Regulators will use all options for robust enforcement action and will continue to prioritise action to protect bathing waters and high priority nature sites."
