United Utilities and local campaigners have proposed a £3.6bn project to build a 12-mile tunnel transporting sewage away from Lake Windermere, aiming to end discharges into England’s largest lake.
Building A £3.7 Billion Sewage Tunnel
Wastewater infrastructure could increase by up to 75 per cent across the catchment, connecting roughly 12,800 people to public sewers for the first time. The landmark feasibility study, titled Only Rainwater into Windermere, assessed more than 70 options before narrowing down to two preferred ways forward. The initiative proposes to intercept and divert wastewater away from the lake for advanced treatment, requiring up to 138km of new sewerage network, 35km of highway runoff interception, and 37 hectares of sustainable drainage.
Estimated investment for the preferred solutions ranges between £3.6 billion and £3.7 billion, with projected economic, environmental, and social benefits totaling around £7.5 billion—equivalent to £1.90 of value for every £1 spent. Two funding models have been put forward. Alternatively, a national charging scheme could spread the cost across England, which would add about 35p a month to household bills nationwide while a local model would cost North West customers significantly more.
Campaigners Debate The Coalition Plans
Edward Twiddy served as the independent convener of the coalition, while Nigel Wilkinson chaired Love Windermere.
Rather than spending £2.5bn on incremental interventions that may never fully achieve these outcomes, and that would bring decades of disruption to communities and businesses, this report presents a £3.7bn investment capable of delivering £7.5bn of benefits.
Edward Twiddy, independent convener of the Only Rainwater into Windermere coalition
For me this is a plan on a piece of paper. It is not definitive action and that’s what I want to see. This is the beginning, and the end of this is the moment that sewage stops entering Windermere.
Matt Staniek, founder of the Save Windermere campaign
Protecting The UNESCO World Heritage Lake
Windermere, sitting at the heart of a UNESCO World Heritage Site that attracts almost 18 million visitors every year, holds about 300 billion litres of water, where it can take up to nine months for water entering one end to travel to the other. The lake has suffered from widespread raw sewage and bacterial pollution driven by discharges from United Utilities, including effluent entering via the River Brathay. Nutrient-rich wastewater combined with warmer temperatures have on several occasions in the last five years caused algal blooming that turns parts of the lake a lurid green.
United Utilities chief executive Louise Beardmore described the proposals as a 100 year solution for this lake
and emphasized that the project is about far more than infrastructure, noting that the team also examined international precedents such as the long-term infrastructural transformation of Lake Annecy in France.
United Utilities Tenders 600m Design Contract
United Utilities has issued an invitation to tender for the contract to conduct detailed design work on the proposed project, with the tender notice identifier recorded as 2026/S 000-099229 on the government’s Find a Tender portal. The design and integration contract has an estimated value of £600m, excluding VAT, and is expected to last 13 years starting from April 1, 2027.
The project now enters a detailed design phase, supported by technical reports and business case chapters. A feasibility study was conducted by Jacobs and Mott MacDonald. Ultimately, the decision on whether to proceed with construction will be a matter for regulators and the government once the detailed design is completed. The network around the lake has historically been fragmented, with homes served by a mixture of public wastewater works and private septic tanks that spill raw sewage when overwhelmed by heavy rain, alongside a continuous stream of treated effluent carrying high nutrient levels.