Regulators face pressure to act after further evidence of potentially illegal activity by water companies has been revealed. Analysis of the latest data shows that more than 2,000 overflows owned by a number of companies are discharging raw sewage into rivers and seas at a scale that should spark an immediate investigation into illegal breaches of permit conditions. The Environment Agency and the economic regulator for the water and sewage sectors, Ofwat, are investigating water companies over suspicions of widespread illegal sewage discharges across the network from thousands of treatment plants. The investigations have been going on for more than two years with no findings published and no action taken against water companies or their senior executives. Water companies in England faced a barrage of criticism on Wednesday as data revealed that raw sewage was discharged for more than 3.6m hours into rivers and seas last year, an increase of 105% on the previous 12 months. The scale of the discharges of untreated waste made 2023 the worst year for storm water pollution. Close analysis of the figures shows the scale and number of high discharging and potentially illegal overflows. More than 677 storm overflows owned by United Utilities, 166 Anglian Water outflows, 401 run by South West Water, 182 owned by Southern Water, 240 run by Wessex Water and 493 owned by Yorkshire Water discharged more than 60 times last year. More than 60 discharges a year from an overflow should spark an investigation by the regulator. Forty-seven overflows owned by Thames Water discharged raw sewage more than 100 times. Six Yorkshire Water outflows, 18 owned by South West Water and 20 run by United Utilities discharged raw sewage more than 200 times in the year. The data shows that maintenance of assets and a lack of hydraulic capacity at the treatment plants were the main reasons for high discharging overflows. Maintenance of its assets accounted for 40% of the reasons Thames Water overflows discharged more than 60 times a year, and 49% of the high rate of discharges were because of a lack of capacity in its treatment works. Southern Water said 65% of its high rate overflows were down to maintenance of its assets. A lack of capacity at its treatment works were also the main reasons for high levels of sewage discharges from overflows owned by Northumbrian Water, Yorkshire Water and United Utilities. Peter Hammond, the academic who first identified the scale of illegal sewage spills by water companies, said: “The 2023 summary spill data suggests an increase in illegal spilling, especially due to groundwater entering leaky pipes. “Most water companies are withholding the data I need to investigate this further and using the excuse that there are ongoing investigations by the EA [Environment Agency] and Ofwat.” James Wallace, the chief executive of River Action, said the shocking data on sewage discharges was a final indictment of a failing industry. He said: “We urgently need the environmental regulators to be reformed and for failing water companies like Thames Water to be refinanced and restructured, putting people and planet above profits. “In this general election year, we urge water bill payers to vote for a party that commits to cleaning up our rivers and securing abundant water for everyone.” It is understood the new data is being examined as part of the investigations into illegal sewage dumping by the regulators. But there is no timescale on when these inquiries will publish findings or take action. An Ofwat spokesperson said: “We have strengthened rules to allow us to take enforcement action against companies that pay dividends to shareholders where their environmental performance does not meet our expectations. “Where companies fall short, we act. Over recent years, we have imposed penalties and payments of over £300m and we currently have our biggest ever investigation under way with live investigations into six companies.” A Yorkshire Water spokesperson said: “We are committed to improving our region’s rivers and were disappointed about the number of discharges in 2023. This increase is due to the wet weather experienced in the 12-month period, which included 11 named storms. The weather experienced in the region in 2023 included a very wet summer and prolonged heavy rainfall towards the end of the year resulting in groundwater infiltration into the sewer network. “We know there is more to do, and we are making headway with a £180m programme to reduce discharges across the region by April 2025. Work is in progress on 62 projects that will reduce discharges from some of the most frequently operating overflows, with more to follow later in the year. This is just the start of a long-term programme to reduce the impact of wastewater on the region’s watercourses and we have submitted plans to Ofwat that outline a further £1.19bn investment in overflow reduction between 2025 and 2030.” The director for wastewater operations at Southern Water, John Penicud, said: “Slashing the number of storm releases is a top priority for us – and our customers. Last November we announced our £1.5bn storm overflow reduction plan which will combine innovative engineering with nature-based solutions. “We are extensively relining sewers, to keep sewage in and rainwater out, and our storm release reduction pilot schemes have already proved that nature-based systems can have a real impact.” A Thames Water spokesperson said: “We regard any untreated discharges as unacceptable and we are committed to stopping them from being necessary, with the assistance of our regulators. Storm discharges are closely linked to rainfall and groundwater conditions and our region experienced above average rainfall for most of 2023, which saw an increase in the frequency and duration of storm discharges from our sites compared to 2022.” South West Water said: “We are serious about tackling storm overflows and change of this scale takes time, ambition and increased investment – and that is why we are investing £850m in our region over two years. “The increase in the storm overflow spills this year can be accounted for by the amount of named storms and weather warnings in 2023. It’s clear we need to redesign our systems, which we are already doing.” A Wessex Water spokesperson said: “Storm overflow discharges increased last year due to exceptionally wet weather, preventing properties from flooding. Hundreds of these overflows are affected by groundwater, with tests showing these discharges are cleaner than the standards set for treated sewage discharges. “While overflows are licensed to operate automatically, we agree they aren’t fit for purpose in a 21st-century sewerage system and are currently spending £3m a month to progressively improve them – with plans to more than double that investment if approved by our regulators.” Mark Garth, the director of wastewater services at United Utilities, said: “I understand and share people’s concerns and the need for change and that is why we are proposing a £3bn programme to tackle storm overflows in the north-west between 2025 and 2030. “Since 2020, even with the increased coverage of monitors and high rainfall, we have achieved a 15% reduction in storm overflow operation. This is thanks to our voluntary investment in our Better Rivers Programme, improved operational processes and an early start on our proposed £13.7bn business plan.” The Guardian approached Anglian Water and United Utilities for comment.