Bathing water quality across most of Windermere is poor throughout the summer, indicating high levels of sewage pollution, according to a comprehensive analysis of water quality in England’s largest lake.
High levels of bacteria found in human faeces – Escherichia coli (E coli) and intestinal enterococci (IE) – indicating sewage pollution, were found to be highest in the summer months, when Windermere is used heavily by holidaymakers for swimming and watersports.
The results come from the largest survey of water quality across the lake, which involved 350 citizen scientists taking more than 1,000 samples over two and a half years in the Big Windermere Survey.
The results, published on Tuesday, include data on water quality from many areas of the lake that have not previously been analysed for water quality.
The analysis shows that in summer concentrations of E coli and IE bacteria in the north-west, north-east and south-west areas of the lake – where some of the most popular tourist locations such as Ambleside and Bowness-on-Windermere are situated – were consistent with poor bathing water quality.
Bacteria concentrations peaked in the summer, but the analysis showed high levels throughout the year.
High levels of phosphorus were also found in sampling, with the north and south areas of the lake meeting standards for moderate rather than good.
Healthy lakes and rivers should have low levels of phosphorus, to support plants and wildlife. Under the water framework directive, which governs the monitoring of UK waters, the government is signed up to a target to achieve at least “good” ecological status in all water bodies by 2027 – including for phosphorus concentrations.
Only 14% of England’s rivers and lakes meet good ecological standards.
Simon Johnson, the executive director for the Freshwater Biological Association, which developed the testing project with Lancaster University, said: “The evidence is clear and must lead to decisive action to improve water quality. We must all work together to transform the future of Windermere and deliver a cleaner, healthier and safer water body for all life to thrive.”
The environment secretary, Steve Reed, has promised to clean up Windermere after criticism over the volume of sewage being pumped into it. As well as legal discharges of treated sewage into the lake by United Utilities, a BBC investigation found it also illegally dumped millions of litres of raw sewage into the watercourse.
The Lancaster University survey found maximum median concentrations of E coli and intestinal enterococci were found at the popular tourist location of Bowness Bay, where levels were five and seven times the concentration respectively for all sites across the whole of Windermere.
The main sources of bacteria and phosphorus are from treated and untreated sewage discharges from water company sites, agricultural runoff and private septic tanks. Around the Windermere shoreline, Waterhead, Millerground, Bowness Bay, Belle Isle, Mitchell Wyke Bay, the south-western shore sites, and near the River Leven sewage outflow, had consistently high concentrations of both phosphorus and at least one bacterial parameter.
Johnson said Windermere was home to a number of rare and increasingly threatened freshwater species. “Without decisive action to improve water quality, this species and potentially many more will face a steady and devastating decline.
“We hope these findings will not only advance scientific understanding of Windermere’s water quality but also play a pivotal role in shaping future strategies to protect and enhance the health of the lake and its surrounding catchment.”
Matt Staniek, who founded the Save Windermere campaign, said the results were damning. “Finally we’re seeing science in the catchment that hasn’t been manipulated by vested interests or shaped by those taking money from the water company,” he said.
“The evidence on the ground is clear and it confirms what local people have known all along: Windermere is in crisis because of sewage pollution. Now we need action from this Labour government following their commitment to end sewage pollution in Windermere.”
A United Utilities spokesperson said:
“United Utilities is wholeheartedly committed to playing our part in continuing to improve the water quality in the lake. Our teams are working at pace to complete multiple projects to treat wastewater to the highest standards possible as well as significantly reducing discharges from the six storm overflows that discharge into the Lake. This builds on our previous investment that has helped cut the amount of phosphorus entering the lake from our own operations by half.
“We are also working with all other organisations and individuals that impact water quality in the lake to help deliver the step change we all want to see.”