Suspected illegal dumping of raw sewage into Windermere took place on up to 70 days in 2022, a year in which campaigners said the lake had its worst summer of harmful algal blooms, according to analysis of data released under environmental information rules. Prof Peter Hammond, whose research first identified the scale of illegal raw sewage discharges from English water companies, has analysed detailed data on spills and treatment by United Utilities, which was released by the Environment Agency. His analysis concluded that permit conditions at three United Utilities treatment works and one pumping station that feed into Windermere were breached on up to 70 days over the year. Breaches of permits are illegal, according to the EA, which is involved in a criminal investigation into potentially illegal discharges from more than 2,000 water company treatment plants across England. In the summer of 2022, blue-green algae covered much of the north shore of Windermere, which is England’s largest natural lake and a world heritage site, in what campaigners said was its worst incidence of the algal blooms. The Environment Agency says blue-green algae can produce toxins that can kill wild animals, livestock and pets and harm people. The blooms damage the biodiversity of a lake by blocking sunlight from reaching plants in the water and using up oxygen, which can suffocate fish and other creatures. Matt Staniek, of the campaign group Save Windermere, requested data from the Environment Agency on spills and treatment at water treatment works at Ambleside, North Sawrey, Grasmere and a pumping station at Hawkshead. Hammond’s analysis found that discharges of raw sewage took place in breach of permits across the year. There were breaches over 15 days at Ambleside, 21 days at North Sawrey, up to 12 days at Grasmere and up to 22 days at Hawkshead. United Utilities rejected the conclusions. It said it had not yet installed monitoring equipment to calculate flow accurately at the sites and said either the methodology was flawed or the analysis drew on an incomplete dataset. Hammond’s analysis suggests the water company was discharging raw sewage before the treatment works had reached their capacity, and not continuing to treat sewage as required by permits under so-called flow to full treatment rules. If sewage is released from a treatment works, the works has to carry on treating sewage at a minimum rate. If it does not, it is in breach of its permit. The EA permits the release of untreated raw sewage to help treatment works cope during heavy rainfall. According to EA data, raw sewage was dumped into Windermere for 5,904 hours over a period of 246 days in 2022. Hammond’s work assesses that up to 70 days of these releases were potentially illegal. Staniek is campaigning for United Utilities to end all sewage releases into the lake. He cites the investment and work carried out in France at Lake Annecy to stop sewage polluting the lake. “Last year alone United Utilities returned £300m to their shareholders and yet we have still not seen a solution or adequate investment to ensure the long-term protection of Windermere,” he said. “Windermere is being exploited and this has to end.” The Cumbrian Wildlife Trust says levels of phosphorus entering the lake have increased dramatically above what should be expected in a rocky, nutrient-poor catchment. A large proportion of the phosphorus entering the lake comes from wastewater treatment works releasing untreated and treated sewage. The trust says wastewater is discharged into Windermere and its tributaries from United Utilities wastewater works as well as about 1,900 septic tanks and private sewerage systems, which are not controlled by the water company. South Cumbria Rivers Trust estimates that 30% of the phosphorus input into Windermere comes from agricultural runoff. The trust says there are worrying signs of the lake’s deterioration. United Utilities has announced a £13.7bn investment plan for 2025-30. Like other water companies, it is seeking permission from Ofwat to make customers pay for the infrastructure. The company said: “We do not recognise these figures and we have not been given sight of the data or calculations that were used. The monitoring equipment needed to calculate flow accurately is not yet available at all of these sites and therefore we can only conclude that the figures have been derived from the application of a flawed methodology to incomplete datasets.” The Environment Agency said: “We are absolutely committed to improving the water quality in Lake Windermere, which is why we are working closely with the local community and a range of partners to reduce pollution from different sources. We are currently analysing data for more than 10,000 storm overflows for 2022; if there is any evidence that permits have not been complied with, we will take action. Our enforcement has already led to over £150m in fines since 2015. We are also conducting our largest ever criminal investigation into potential widespread non-compliance at thousands of sewage treatment works.”