A major citizen science project has shown elevated phosphorus and bacteria levels at locations around Windermere and its catchment this summer.
The findings are among newly published results from the fifth Big Windermere Survey, conducted in August 2023. This marked the start of the second year of the programme, led by scientists at Lancaster University and the Freshwater Biological Association, which is designed to investigate water quality in Windermere, England's largest natural lake.
Water samples collected during the Survey are analysed for the concentration of bacteria and of nutrients, including phosphorus. Compared to previous results, data from the latest Survey reveal higher concentrations of phosphorus at many lake sampling sites in the catchment. For Windermere itself, only 3% of samples collected from the lake's shoreline contained sufficiently low concentrations of phosphorus to meet default standards for 'High' or 'Good' status under UK legislation.
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. However, 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 and a lead investigator on the project, said: "Concentrations of bacteria are obviously important to those using the lake for recreation, particularly for swimming. Our data show 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 scientists say 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.
The latest survey was conducted on Sunday 13th August and during the school summer holidays, 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 and also a lead investigator on the project, 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.
Emma Kelly, Windermere Project Officer at the Freshwater Biological Association, said: "Across the five Big Windermere Surveys since June 2022, more than 300 volunteer citizen scientists have collected 600 litres of water from the catchment, enabling over 2,500 water quality analyses to be undertaken. We continue to use evidence from the Big Windermere Survey, generated by our fantastic network of citizen scientists, as part of our work with organisations such as the Environment Agency and others in the Love Windermere Partnership, in order to improve water quality within the catchment."
The full dataset from the latest Big Windermere Survey is openly available to the public via the following link to Cartographer. Results from the four previous Surveys are openly available from the Freshwater Biological Association website: Big Windermere Survey
The next Big Windermere Survey will take place on Sunday 26th
