WELSH Water’s illegal and “sickening” spillage of untreated sewage is outrageous, campaigners said today, after an investigation was launched into the company.

Natural Resources Wales said it was examining the severity and frequency of permit breaches by the water firm.

The company admitted that between 40 and 50 of its wastewater treatment plants are currently operating in breach of their permits after being shown data by an environmental campaigner.

Analysis by Professor Peter Hammond, from the campaign group Windrush Against Sewage Pollution, showed the worst offender is the Cardigan plant in west Wales, which spilt untreated sewage on 1,146 days from the start of 2018 to the end of May 2023.

Surfers Against Sewage’s Jade Chapman said: “We are outraged at this sickening behaviour by Welsh Water, who have been hiding their polluting practices under the cover of darkness for decades — just like they’re hiding behind their ‘not for profit’ status.

“Their CEO pay packets have long reflected that this is a business profiteering from pollution.”

Welsh Rivers Union founder Kim Waters called for prosecutions, saying: “Once again, this was highlighted three years ago in a BBC Panorama documentary when Dwr Cymru [Welsh Water] and Natural Resources Wales failed to protect Welsh rivers and biodiversity, and their statutory legal duties.”

Matthew Topham, lead campaigner at public ownership campaign group We Own It, said: “Despite being notionally not-for-profit, Welsh Water still suffers many of the ills of privatisation.

“It must borrow on private markets and pay out money to these profit-hungry creditors.”

Mr Topham said that under public ownership, the cost of borrowing to invest would be slashed, “leaving us free to reinvest the savings to put people and the planet over profit.”

“Almost nowhere in the world runs water the wacky way we do in England and Wales, and for good reason: water is a vital public service,” he said. “It belongs in public hands.”

Water treatment works are allowed to discharge untreated sewage in order to ensure it does not become overwhelmed during heavy rain, but this overflow level is regulated by permit.

A Welsh Water spokeswoman said: “We always aim to resolve any issues as quickly as possible, to limit any impact for both the environment and our customers.”

An Ofwat spokeswoman said the regulator is currently investigating all 11 water and wastewater companies for potential failures.