19 May 2025

Lakes Parish Council and Ambleside Action for a Future water group have teamed up to monitor water quality at Waterhead, Ambleside – a place where local residents, visitors, and their dogs regularly access the lake. 

From Easter to October, lake water collected by volunteers from the end of the public pier at Waterhead is being sent away to be professionally tested at Simplex labs to accurately measure the amount of the faecal indicator bacteria E. coli and Intestinal Enterococci present.

There are no designated bathing areas at the northern end of Windermere, so the Environment Agency does not offer weekly water quality monitoring in the Ambleside area.

However, on three occasions, including August 2023 and September 2024, the quarterly Big Windermere Survey ran by the Freshwater Biological Association (FBA) and Lancaster University found elevated levels of E. coli and Intestinal Enterococci in the lake alongside Waterhead, Borrans Park and Birdhouse Meadows sufficient to render the bathing water status ‘poor’ – a status where you’d be advised not to swim if this area was a designated bathing water. In addition, blue-green algae blooms have recently been a regular occurrence.

The Waterhead E. coli Testing (WET) project has been set up to test weekly for E. coli and Intestinal Enterococci and communicate the results to the public via two noticeboards situated at Waterhead and on the WET webpage – aafaf.uk/wet .

The official UK Bathing Water Quality assessments of Excellent, Good, Sufficient and Poor, published by the Environment Agency, are based on measurements of E. coli and Intestinal Enterococci sampled weekly at designated bathing waters over the summer period and are calculated using the last four complete years of data. As such they provide an indication of the typical conditions that a bather may expect, but provide no information about current levels of risk.

The US Environmental Protection Agency (EPA) has a different method to process the same bacterial data. It uses a rolling 30-day period of measurements to focus on current risk levels. It calculates two values: firstly, the mean of the measurements in the last 30 days, and secondly, a statistical value (‘STV-90’) which takes into account how the measurements have varied in that 30-day period which indicates the likelihood of a temporary peak in bacterial levels on any given day.

Thresholds are set by the EPA for each value, based on studies which show that no more than 32 in 1,000 people would be expected to fall ill after bathing in water of this quality, and neither threshold must be exceeded for either bacterial type for a bathing area to pass. There are only two designations – ‘pass’ or ‘fail’.

As we do not have four years of previous data for the Waterhead site, the WET project decided that it could not legitimately use the EA’s system to assess the status of the water, and since the aim of the WET project is to provide timely information to water users, it was decided that the EPA’s methodology was a better fit for our needs. For each bacterial type we produce two graphs: one for the mean value and the other for the STV-90 value. If the actual value exceeds the threshold on any one of the four graphs, the result is a fail.

For more information, and for full results of the testing go to aafaf.uk/wet