Friends of Derwent Water

For bathing water designation, the water is being tested for two types of bacteria which cause illness in humans and animals, these are intestinal enterococci and E. coli. 

Possible sources of these bacteria are poo from humans and animals or birds: from sewage systems, septic tanks, wildlife and livestock (sheep) poo.  The relative contribution of each of these sources is not clear at the moment. 

They can cause stomach upsets if contaminated water is ingested and infect cuts and wounds. 

Blue green algae blooms are encouraged by heat, standing water, high level of nutrients (phosphates and nitrates) which are associated with agricultural activities.  This is a different problem, but also makes bathing water quality poor.  Algal blooms are identified by eye and measures taken to warn lake users as appropriate (generally not to allow dogs or humans to swim). Advice for the public and landowners about blue green algae can be found on gov.uk. If you see evidence of algal blooms, please report this via the Environment Agency’s Incident Hotline (0800 80 70 60) or use the CEH Bloomin’ Algae app.

The Environment Agency’s recent testing has classified Derwent Water as “Poor” for bathing, meaning conditions are currently not suitable for swimming.

We don’t know.  At the moment we only have information for Crow Park.   In the 2025 bathing water season, the Environment Agency will be monitoring other areas which are popular with swimmers and watersports enthusiasts, such as Calf Close Bay.    This data is a first step in improving water quality – once we know more about the sources, it will help us to target actions to solve the problem.    It is possible that different parts of the lake will be more or less contaminated depending on the proximity of waste water discharges, wildlife, and human behaviour (toileting outside and dog poo left on the lakeshore).

The water quality was designated poor in 2024 because there were 3/20 readings where levels of bacteria were higher than acceptable levels and posted a risk to health. These higher readings were associated with high rainfall events.

The pollution affecting bathing water quality is from faeces (poo) – bird, human and/or animal. Other pollutants affecting the lake include nutrients e.g. phosphates and nitrates.

Swimming is a personal choice. However, based on current bathing water quality data, the Environment Agency advise against bathing at Crow Park. If you do swim in Derwent Water, please practice safe swimming habits (e.g. heads up swimming, washing thoroughly afterward, and covering any cuts).

Much of Derwentwater, and the land surrounding it, is owned by the National Trust, with some land also owned by private landowners. All those who live, work and play on or near the lake, and especially those who benefit economically from it, have a collective responsibility for Derwentwater. The National Trust own the land at Crow Park and Cumberland Council have responsibility for the jetties.

West Cumbria Rivers Trust is collaborating with partners like United Utilities, the Environment Agency and the National Trust to undertake more comprehensive testing. Once we have a clear scientific understanding we may be able to identify possible causes. Once we know the causes, we can work closely with partners to implement effective solutions.  This may involve things like upgrading septic tanks, or changes in land management near the lakeshore.

As a designated bathing water site, Crow Part at Derwent Water will be monitored weekly by the Environment Agency during the bathing season (May to September). Results are published on the Swimfo website. The Environment Agency will also be monitoring at other locations around the lake. These are investigative samples and will not be used to classify the bathing water.

You can contribute by ensuring you dispose of human and pet waste properly, not feeding the wildlife (which can contribute to pollution as the numbers can increase and with that the amount of poo), and supporting our campaign to restore the lake. Every small step helps us move toward a healthier environment.

Detailed results from the 2024 bathing water season are available on the Environment Agency’s Swimfo website. Results from the 2025 bathing water season will be published throughout the bathing water season. You can also visit the Environment Agency’s Water Hub to find out more about bathing waters and other issues affecting the water environment.

Please reach out to West Cumbria Rivers Trust below. We welcome your feedback and are committed to keeping the community informed.