A new research study has found a direct correlation between visitor numbers and algal spikes in Windermere, with algal growth also exacerbated during prolonged warm, dry weather periods.

The research by Save Windermere, in partnership with Map Impact and backed by the UK Space Agency with a Climate Services Grant, was carried in a groundbreaking data collection programme to study England's largest freshwater lake.

Due to the type of farming in and around Windermere and the type of land use in the catchment, the study found no correlation between agricultural input and algal spikes in Windermere.

Prior to the study, no investigation had delved into the correlation between human activity in the area and its impact on the lake.

Satellite data can provide clearer information about how natural resources are changing

Dr Paul Bate, Chief Executive of the UK Space Agency commented:

“Map Impact’s report, focusing on one of the UK’s most iconic and important lakes, demonstrates how this 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.”

The report is the outcome of months of meticulous analysis by Map Impact and the collection of thousands of images and data points.

The project specifically focused on examining the concentration of chlorophyll-a in the lake, using satellite data from various sources. Chlorophyll-a in freshwater not only serves as an indicator for algal growth and concentration, but is also a reliable indicator of phosphorus concentrations.

Windermere is under threat from excessive phosphorus, which facilitates the proliferation of algal blooms. The danger of extensive algal blooms lies in their potential toxicity to both humans and wildlife if ingested, as well as their ability to deplete oxygen levels in the water, potentially resulting in mass fish kills, especially in large blooms.

The satellite imagery was complemented by data from one of the UK's largest mobile networks, with anonymised cellular data used to gauge the number of people within the Windermere catchment at given points of time. Save Windermere said this had revealed “some rather startling figures.”

Whilst the resident population of the Windermere catchment stood at around 35,000 during the COVID-19 lockdown, the lifting of COVID-19 restrictions saw a massive influx of visitors to the National Park.

On certain days in the summer of 2020, there were over 300,000 people in the catchment alone. The increased loading of people around the lake was directly correlated with the increased presence of algae in the lake. Even when numbers returned to ‘normal’ in 2022, Windermere still saw over 200,000 people in the catchment on given days.

Climate change making nutrient removal imperative to remove resilience

Despite the slightly lower population figure in 2022, the lake witnessed a more severe algal bloom due to higher water temperatures in the lake. The study underscores the significance of temperature on algal growth. With a 1.7-degree rise in annual average temperature over the past 70 years alone and the heightened risk of droughts due to climate change, the threat escalates, making nutrient removal imperative to ensure resilience.

Photo:Algal Bloom at Waterhead, Ambleside August 2022

Save Windermere commented:

“This situation is instead a result of Environment Agency failings and insufficient, inadequate investment by the billion-pound water company, United Utilities (UU). We have not seen enough investment to ensure sustainable development and as a result, our lake is not adaptable to climate change.

“We contend that not only has investment made thus far not been sufficient to ensure the adaptability of the lake to climate change, but that the sewage infrastructure also struggles to cope with these surges in population.”

The environmental organisation has highlighted the fact that United Utilities had declined to share any data for the project, despite the water company’s ownership of the vast majority of the infrastructure in and around Windermere.

According to Save Windermere, the data they had requested would have enabled it to determine the full contribution of United Utilities to the algal spikes in the lake.

The project builds on Save Windermere’s existing scientific collaborations. To date data collection and analysis in collaboration with Windrush Against Sewage Pollution (WASP), has uncovered instances of illegal sewage discharges into Windermere and its wider catchment, whilst its invertebrate sampling programme with WildFish has shown significant declines in invertebrate abundance and diversity on several river sites in the catchment.

Save Windermere said that WASP’s analysis has identified at least 234 days with early spills of untreated sewage by United Utilities to Lake Windermere and catchment watercourses between 2018 and 2022, highlighting a lack of capacity, whilst the ongoing work with Wildfish has demonstrated the impact of United Utilities discharge points in the Windermere catchment in the absence of effective regulation.

With these longer-term data collection projects now looking at the overall health of Windermere, it has been clearly demonstrated that there is a correlation between visitor numbers and algal growth which underscores the necessity for a long-term infrastructure investment plan surpassing current proposals, addressing both untreated and treated sewage.

Click here to download the summary report

Click here to access the detailed technical study