Floods of tourists turning Windermere green say scientists
Scientific study shows that high tourist numbers and hot summer weather are turning Windermere green.
The research released this week has been backed by the UK Space Agency and is the first of its kind to look at the correlation between human activity and its impact on algal growth in the area.
The project collected thousands of images of the iconic body of water over five years and has been carried out in partnership between campaign group, Save Windemere and Map Impact.
They found there is a "direct correlation" between increased visitor numbers and increase algal growth on the lake.
What causes algal growth?
The study found that sewage spills are one of the main factors impacting the ecology of England's largest lake.
Campaigners say the sewage infrastructure struggles to cope with the surges in population during the summer.
On peak days during tourism season, there more than 300,000 people in the area, compared to the resident population of just 35,000.
Water companies are legally allowed to discharge excess wastewater into the sea and rivers in times of heavy rainfall when the sewage systems overflow.
Windrush Against Sewage Pollution (WASP) claims it has uncovered instances of sewage discharges into Windermere and its wider catchment since 2018, through its analysis of United Utilities' data.
Their analysis identified hundreds of early spills of untreated sewage to Lake Windermere and the catchment area between 2018 and 2022, claiming these highlight a lack of capacity in the current sewage system.
Algal growth has also been shown to worsen when lake temperature increases and there are prolonged periods of warm, dry weather.
Agriculture has also been shows to impact algal growth from the run-off of fertilizers into bodies of water, but the study found "no correlation between agricultural input and algal spikes in Windermere".
Matt Staniek, Founder of Save Windermere said: "This isn't just about visitor numbers or climate change; it's about the failure to adequately manage and invest sufficiently in sewage infrastructure, essential for the lake's resilience to these pressures.
"With a clear link between human activity and algal growth, action is imperative.
"Save Windermere is calling for complete removal of all sewage from Windermere.”
An Environment Agency spokesperson said: “Windermere is affected by pollution from a range of different sources, including sewage discharges from waste water treatment works, storm overflows, septic tanks and road and agricultural run-off.
"Recent data shows a 30% reduction in phosphorus – which can lead to algal blooms – entering the lake since 2020, and the lake’s bathing waters were rated ‘excellent’ in 2023, but we know there is more to do.
“We are absolutely committed to improving the water quality in Lake Windermere.
"That is why we are working closely with the local community and a range of partners to reduce pollution from all sources as well as reviewing wastewater treatment works permits within the Windermere catchment.”
A spokesperson from United Utilities said: “Our wastewater treatment works are sized to treat the sewage from maximum population numbers at peak times, and use the highest treatment standards including phosphorus removal and UV treatment to kill bacteria.
“We carried out a feasibility study that has already been shared with key local stakeholders and we are keen to engage with anyone who might want to investigate this further.”
Dr Paul Bate, Chief Executive of the UK Space Agency said: " Map Impact’s report, focusing on one of the UK’s most iconic and important lakes, demonstrates how data can be used to give us clearer information about how the natural resources around us are changing, helping communities and decision-makers take tangible steps towards improving pollution levels and mitigating their impacts.”
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