Image description: Sailboats cutting across the surface of lake Windermere with mountains rising in the background. Photo by JOGphotos on Unsplash

Water company United Utilities is proposing building an underground tank to improve the water quality of England’s biggest freshwater lake – Lake Windermere.

The company says the facility, which would hold the equivalent of four Olympic-sized swimming pools, would reduce the frequency with which storm overflows, designed to act as relief valves when the sewerage system is at risk of being overwhelmed, are used.

If it gets planning permission, construction of the tank would begin on land off Glebe Road, Bowness-on-Windermere in 2027, and should be completed by early 2030. United Utilities says it is investing £200 million across the Windermere catchment over the next four years, part of “the largest investment in water and wastewater infrastructure across the North West for a century”.

A previous BBC investigation found United Utilities dumped millions of litres of raw sewage illegally into Windermere in Cumbria over a three-year period between 2021 and 2023.

Although reportedly “sceptical” about the plan’s effectiveness, the plan has reportedly been cautiously welcomed by sewage pollution campaigner and founder of Save Windermere, Matt Staniek: “Any investment is good because it’s needed but United Utilities needs to stop putting any sewage, treated or untreated, into Windermere.”

Two drop-in events about the new tank are being held on 16 June at the Belsfield Hotel in Bowness-on-Windermere and on 17 June at the Marchesi Centre in Windermere, between 1600-1900 BST.