Water companies discharged raw sewage into rivers and seas via their storm overflows more than 300,000 times last year, according to new data presented to the high court. The new figures came as – in a separate hearing – Thames Water was fined £3.34m for sewage dumping. The vast majority of the releases of raw sewage were illegal, the high court heard. The discharges had happened because of a lack of capacity at treatment works run by water companies and had been in breach of the law, it was told. The new figures come as water companies are under huge pressure to invest in ageing infrastructure and high interest rates are raising costs on their billions of pounds of debt. Ofwat CEO David Black told peers on Tuesday that the whole of the water sector had levels of debt that were too high, and it had to reduce. Speaking before the House of Lords Industry and Regulators Committee, Black said that Thames Water would have to raise billions more from its shareholders in addition to the £1.5bn already promised. Black said the company’s financial resilience had become acute becauses of its persistent poor performance and very high levels of debt. The data on sewage – which has yet to be published by the Environment Agency – revealed raw sewage dumping by water companies had reduced slightly. In 2022 water firms pumped raw sewage into rivers and the sea from storm overflows 301,000 times, over 1.75m hours. This compares with 372,533 over 2.7m hours in 2021. But storm overflows are supposed to be used only in exceptional circumstances such as unusually high rainfall to release pressure in the sewerage system. In 2022, however, 52% of the raw sewage discharges from the 14,000 storm overflows that were monitored spilled more than 10 times, the court heard. Eleven per cent discharged raw sewage more than 60 times. As such they had been in breach of the law – the urban wastewater (England and Wales) regulations 1994. “You see the enormous scale of the problem,” said David Forsdick KC, representing the environmental group WildFish. He said the majority of the discharges – 75% – into waterways were because of a lack of hydraulic capacity at treatment works. The high court heard that most raw sewage discharges from storm overflows had been illegal for decades. “Data unambiguously demonstrates that most occur other than in exceptional weather events and have thus … been unlawful for years,” said Forsdick on Tuesday. WildFish is challenging the government’s new £56bn plan to reduce the scale of storm overflows, which involves customers paying for the investment in increased water bills, saying it is unlawful. Estimates of bill rises to pay for the fix range from £91 a year to reports that water bills will go up by 40% to fund the investment needed. Lawyers for WildFish say water companies must pay to fix illegal sewage discharges rather than pass the cost to customers because they are in breach of compliance rules. Ofwat, the regulator, says companies, not customers, must pay to bring their infrastructure up to compliance. Nick Measham, the chief executive of WildFish, said: “It is time for the government to … make the water companies do what they have promised to do, and have been required to do by law, for nearly 30 years. “This must be at their own expense. Our wild fish, our rivers and all of us have had enough.” The new figures were revealed as Thames Water, which is seeking billions of pounds in an equity bailout from its shareholders as it struggles with £14bn of debt, was fined £3.34m for a “reckless” incident in which millions of litres of undiluted sewage was pumped into rivers near Gatwick, killing 1,700 fish. Judge Laing KC told Lewes crown court the company – which pleaded guilty at an earlier hearing to four breaches of permits – deliberately misled the Environment Agency during its investigation. Thames Water had allowed untreated sewage to pour into the rivers near Gatwick from the lagoon outside of storm conditions illegally. A two-day sentencing hearing at Lewes crown court was told there was a “significant and lengthy” period of polluting the Gatwick Stream and River Mole between Crawley in West Sussex and Horley in Surrey on 11 October 2017. Cathryn Ross, the interim co-CEO of Thames Water, said: “We are deeply sorry for the entirely unacceptable pollution incident into the Gatwick Stream and River Mole six years ago. The incident occurred due to the running of a storm pump in error.” She added: “It should not have happened, and we deeply regret the incident. I would also like to express my sincere apologies for those aspects of our response to the incident six years ago that led to the finding that we misled the regulator. We fully accept that we made significant errors and exercised poor judgment at the time, and we are genuinely sorry for that.” The company said it had taken a number of steps in response to the incident, including making voluntary payments totalling £1m to three local organisations to fund projects, committing £32.9m to a site improvement plan, and better staff training. Jim McMahon, the shadow environment secretary, said: “This is a significant fine for Thames Water, which highlights the seriousness of the offence. But it shouldn’t have taken five years to get to this point, which is why Labour’s plan for water would deliver automatic fines for sewage discharges.” The Liberal Democrats’ environment spokesperson, Tim Farron, said: “It’s time to rip up Thames Water and reform it from top to bottom. This scandal-ridden firm has put profit first, leading to animals being killed.” In a separate legal challenge also being heard this week, the Good Law Project is supporting the Marine Conservation Society, Richard Haward’s Oysters and the surfer and activist Hugo Tagholm, who argue that the government’s strategy allows water companies to pollute waters and beaches for another 27 years. Lawyers for the trio say the government’s storm overflow reduction plan will allow the discharge of untreated sewage into water bodies (including coastal waters) to continue for decades – up until 2050 – and is insufficient to meet legal obligations. In its legal defence the government said the environment, food and rural affairs secretary had acted lawfully when preparing and publishing the storm overflow plan, and argued its plan went beyond any existing legal requirements to eliminate harm from storm overflows, was the largest infrastructure investment plan to improve water quality, and contained clear provisions to avoid any disproportionate impact to customer bills.