Calls are being made for better water infrastructure after new research found high numbers of visitors are turning Windermere green.
The research – funded by the UK Space Agency – has discovered a link between influxes of tourists and algal blooming in the water.
Windermere has been turning green due to algal blooms in periods of hot weather more frequently over recent years, which has caused national concern.
Campaign group Save Windermere, which organised and helped carry out the research with environmental charity Map Impact, is linking the blooms to sewage discharge and inadequate water infrastructure.
The campaign argues that current water infrastructure does not support large amounts of visitors and that a long-term water infrastructure investment plan that fully stops sewage discharge entering the lake is needed.
According to the new research, up to 300,000 people can visit Windermere in a single day in peak season – the equivalent of a small city descending on the town.
Despite the calls for change – United Utilities has insisted that its wastewater plants can cope with large influxes of tourists during peak seasons.
How was the study carried out?
Map Impact and Save Windermere used anonymised mobile phone data to compare the number of people in the area with satellite data showing the levels of chlorophyll in the lake.
Chlorophyll is found in algae and is an indicator of the presence of algal bloom.
The mobile phone data allowed the team to estimate the number of people in Windermere at given points in time – which also highlighted that the area can be subject to over 300,000 visitors on a single day.
The group said it found direct correlation between visitor loading and algal growth in the lake and that algal growth is worsened by periods of hot weather.
It also found no correlation between agricultural input and algal spikes in Windermere.
The research is believed to be the first time a scientific study has explored the impact of human activity on the lake.
Save Windermere and Map Impact also approached United Utilities to request sewage data to support the study – but the water company declined to provide the data.
Matt Staniek, founder of the Save Windermere campaign, said: “You don’t have to have data from United Utilities to ask realistically, can the sewage works cope with that amount of visitors?
“They’re largely built for a rural population and it’s like the entire city of Nottingham descending on the area and there’s nothing stopping that from happening again.
“This isn’t just about visitor numbers or climate change, it’s about the failure of the Environment Agency and United Utilities to adequately manage and invest sufficiently in sewage infrastructure, essential for the lake’s resilience to these pressures.”
United Utilities declined to comment further.
So, are tourists fully to blame for the green water?
Matt said that the findings of the new study were not ‘blaming’ tourism.
He added that the findings highlighted a need for strengthened water infrastructure that supports large numbers of people visiting the area, while also putting a stop to sewage discharge entering Windermere.
He said: “This isn’t about people coming here, this is about infrastructure. From a campaign perspective we want people to come here. We’re lucky enough to be based here in one of the most incredible places in the entire world.
“This is about inadequate investment over time that has not ensured the sustainable growth of the area and it’s about the failure of the regulator. This is what it all comes down to.
“We’re putting the same message out, which is stop putting sewage in the lake. We need a realistic long term infrastructure investment plan.”
Last year, United Utilities carried out a feasibility study to assess options to remove all discharges from the Windermere catchment.
The water company said diverting all sewage away from the lake could cost up to £6.4 billion.
A spokesman added: “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.
“To contribute to the debate about a ‘discharge-free’ solution with no treated or untreated United Utilities discharges, no effluent from the 1,800 private septic tanks or from the additional 89 discharge points around the lake that are owned by others, 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.”
Water companies can legally discharge sewage during periods of excess rain. But rising statistics have led to questions about discharges being more routine than the law permits.
The Environment Agency also allows treated effluent to be discharged into the UK’s waters – which while clean, is also high in nutrients that can contribute to algal growth.
An agency spokesman 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 per cent 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 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.”
The EA carried out research last year that found over half of the phosphorus – a key element in nutrients that worsens algal bloom – in Windermere comes from sewage sources including treatment works, storm overflows, septic tanks and private treatment facilities.
