Survey reveals increased pollutants at Windermere

Increased pollution has been found in England's largest natural lake.

Samples from Windermere, and rivers and lakes in its catchment, revealed higher levels of phosphorus in August compared to 2022.

Only 3% of samples collected from the lake's shoreline met minimum standards under UK legislation.

That is according to results of the fifth Big Windermere Survey, a citizen science project led by the University of Lancaster and the Freshwater Biological Association.

It found that the elevated phosphorus concentrations observed in August 2023 are potentially significant for the ecology of the lake, with phosphorus being one factor linked to the growth of algae within Windermere.

For bacteria, around two thirds of samples from the catchment had relatively low concentrations, consistent with standards from the European Union Bathing Water Directive for Excellent or Good bathing water quality.

Although, the remaining third of sites contained higher concentrations of E.coli or intestinal enterococci bacteria.

Dr Lynsey Harper, Windermere Senior Scientist at the Freshwater Biological Association, said: "Concentrations of bacteria are obviously important to those using the lake for recreation, particularly for swimming.

"Our data shows that increases in the concentration of bacteria at certain locations within Windermere and its catchment coincided with collection of samples for the Survey in August this year."

The latest survey was conducted on 13 August, a busy time of year for tourism and the local economy in the Lake District.

At the same time, heavy rainfall within Windermere's catchment leading up to the Survey meant that river and stream discharge, which is the volume of water moving every second, was at the highest level seen across any of the five Big Windermere Surveys to date.

Dr Ben Surridge, Senior Lecturer at Lancaster University, said: "The Survey is not designed to pinpoint individual pollution sources.

"However, heavy rainfall may have increased the input of pollutants, including phosphorus and bacteria, to rivers and lakes from a number of sources in the catchment.

"These include increased release of wastewater from mains sewerage networks and from private wastewater treatment infrastructure, such as septic tanks, and increased runoff from agricultural land and from other land surfaces."

Evidence from the Surveys is being used to inform more detailed investigations and management actions that seek to improve water quality in Windermere.

Scientists at the project have said that it is important to recognise that water quality within rivers and lakes varies significantly through time.

The Big Windermere Survey provides one-day snapshots of conditions across the catchment, in order to capture this variation and to understand the factors that cause it.

Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know...