Lake Windermere turns GREEN thanks to tourists: Shocking footage shows emerald waters as scientists blame visitors for algae blooms in the Lake District
Tourists taking a trip to the Lake District this summer may be looking forward to cooling off in the deep blue waters of Lake Windermere.
But as temperatures rise, holidaymakers may be shocked to discover that Britain’s largest lake has turned a shocking emerald green.
Map Impact scientists now say it may be tourists themselves who are responsible for this annual transformation.
A study funded by the UK Space Agency found that sewage from hundreds of thousands of visitors fuels algae blooms that threaten wildlife and people.
Richard Flemmings, CEO of Map Impact, told MailOnline: ‘We can see a link between increasing numbers of people and increasing algae strength.
Tourists can cause Lake Windermere (pictured) to turn green as their sewage feeds huge algae blooms every summer
Every summer, Lake Windermere begins to turn green as warmer temperatures make algae blooms increasingly likely
In recent years, Lake Windermere has turned alarmingly green each summer as warmer temperatures cause the algae to grow faster.
For example, during a heat wave in 2022, tourists were warned to avoid the waters of Lake Windermere as the lake was overwhelmed by a blue-green algae bloom.
However, the researchers discovered that it is not just the warmer summers that are responsible for this change.
The team compared anonymized phone data with satellite images of chlorophyll levels in the lake.
They found that there was a link between the large numbers of tourists and algae blooms in the following days, whether the weather was warm or not.
Mr Flemmings says: ‘What we see with those peaks in the tourist season are algae events three to five days later.
The researchers found that algae blooms in the Lake District, such as this one in Esthwaite Water, were due to increased numbers of tourists
The sewage from the 300,000 tourists who arrive on some peak days adds nutrients to the water, causing algae to grow out of control
On peak tourist days, the population of the Lake Windermere catchment can increase more than eight times from 40,000 to more than 300,000 in 24 hours.
That equates to a city where the population of Nottingham appears overnight.
With so many people arriving, there is inevitably a huge increase in the amount of sewage produced.
Both treated and untreated sewage contains high levels of phosphorus, a source of nitrates essential for algae blooms.
Although Mr Flemmings notes that this study does not look directly at sewage infrastructure in the Lake District, he says this research ‘underlines the need for action’.
“I think we can conclude that the sewage infrastructure is probably not sufficient for this enormous increase in the number of people,” he said.
A 2023 study found that phosphorus levels increased significantly during school holidays and the summer period, and that increases were particularly high near sewage discharge points.
This suggests that even wastewater discharges may contain enough nutrients to contribute to the formation of algal blooms.
At peak times, the researchers found that the Lake Windermere catchment was visited by eight times as many residents – the same as the population of Nottingham.
A 2023 study found that sewage discharges into the lake in April 2023 (left) and August 2023 (right) were associated with significantly higher phosphorus levels.
In November 2023, another study found that only three percent of water samples collected around the lake met the standards for phosphorus levels under British law.
United Utilities, which manages the Windermere area’s sewage treatment plant, did not comment on whether the algae bloom was related to sewage discharge.
A company spokesperson told MailOnline: ‘Our wastewater treatment plants are sized to treat sewage from maximum population numbers at peak times and use the highest treatment standards including phosphorus removal and UV treatment to kill bacteria.’
The spokesperson added that United Utilities had conducted a feasibility study on a ‘discharge-free’ solution for sewage around the lake.
Algal blooms absorb so much oxygen from the water that they kill fish and other animals. Extremely strong flowers even produce toxins that can be harmful to humans
However, greening lakes are more than just an eyesore, as these algae blooms can be harmful to wildlife and even people.
Mr Flemmings says: ‘If you let those green bits of algae grow very quickly, that means a lot of other things run out of oxygen in the water.
‘This can have a negative effect on wildlife and there is also evidence that algae blooms, when very strong, can have a harmful effect on people swimming or using the lake.’
Some types of algae are known to produce toxins that people can ingest by swimming in the water or even by eating fish that live in the lake.
The toxins found during the 2022 Lake Windermere bloom were described by a top ecologist as being as toxic as cobra venom.
Chemicals produced by some algae have been linked to gastrointestinal illness and liver damage, while others in high doses can be fatal to dogs and humans.