A coalition of national and local organisations has today published a landmark feasibility report setting out how England's largest natural lake could be protected for the next 100 years - the two preferred solutions would require investment of between £3.6 billion and £3.7 billion.

Photo: Algal blooms on Lake Windermere

The Only Rainwater into Windermere feasibility study concludes that it is technically possible to remove wastewater inputs and highway runoff from Windermere and create a future where only rainwater enters the lake.

Developed over the past 15 months by a coalition of regulators, local authorities, community stakeholders, environmental campaigners and the regional water company, the study explores how a catchment-wide solution could address the growing environmental and climate challenges facing Windermere.

The report concludes that a transformational approach is needed to create a resilient wastewater system for a changing climate. Evidence shows that Windermere is already experiencing ecological pressures such as increasing algal biomass, nutrient enrichment and impacts on sensitive freshwater habitats and species.

Rising temperatures will increase these pressures while more intense rainfall places more stress on wastewater infrastructure. While significant investment is already underway, modelling indicates that continued cycles of incremental investment will not restore Windermere's ecological health or provide the resilience needed for the century ahead.

Preferred solutions would require investment of between £3.6 billion and £3.7 billion

The study assessed more than 70 potential solutions before narrowing these to two preferred ways forward. Both would intercept and transfer wastewater away from the lake for advanced treatment, with up to 138km of new sewerage network, 35km of highway runoff interception, and 37 hectares of sustainable drainage. In total, wastewater infrastructure could increase by up to 75% across the catchment, and around 12,800 people could be connected to public sewers for the first time.

Both options include a new tunnel to transfer wastewater to state-of-the-art treatment facilities capable of delivering some of the highest treatment standards in England, ensuring that communities and ecosystems downstream of the lake also benefit.

The feasibility study estimates that the preferred solutions would require investment of between £3.6 billion and £3.7 billion and generate around £7.5 billion in economic, environmental and social benefits, equivalent to approximately £1.90 of value for every £1 invested.

The report says that if the Only Rainwater solution was not built, it is estimated that approximately £2.5 billion of incremental investment would be required in existing infrastructure across the catchment over the next century to address growing environmental pressures.

However, in this scenario, treated wastewater would continue to be discharged into the lake, adding to the nutrient load which contributes to harmful algal blooms, and exposing sewers and treatment works to more extreme climate-related flooding.

The feasibility study identifies a clear pathway to delivery, with an expected seven-year construction programme following detailed design, planning, environmental assessment and regulatory approvals. A key feature of the proposals is the use of extensive underground tunnelling to minimise disruption for local communities, businesses and the landscape.

Coalition calls for continued collaboration between Government, regulators, delivery partners, and local stakeholders to consider findings

The Only Rainwater into Windermere coalition comprises the Environment Agency, Lake District National Park Authority, Love Windermere, Save Windermere, United Utilities and Westmorland and Furness Council.

The coalition is now calling for continued collaboration between Government, regulators, delivery partners, and local stakeholders to consider the findings and explore the next stage of development, including detailed design, planning, environmental assessment and funding arrangements. The coalition remains committed to continued engagement with local communities as the project develops.

Louise Beardmore, Chief Executive Officer of United Utilities, said:

"What makes this work so extraordinary is the unprecedented coalition behind it. Environmental campaigners, local authorities, regulators, community groups and United Utilities have come together with a shared ambition: to secure the future of Windermere for generations to come.

“This landmark feasibility study is clear. Rising temperatures, population growth and increased rainfall demand a transformational approach to create a resilient wastewater system for the future. After assessing more than 70 options, two have been selected to progress into detailed design, with the potential to deliver lasting environmental, social and economic benefits across the catchment.”

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