Dye River Dye: Exposing Monitoring Failures on Cunsey Beck in the Windermere Catchment
Firstly, it’s important to clarify that the tracing dye used in this study is non-toxic and biodegradable. Fluorescein dye, commonly used by the Environment Agency (EA), water companies, and even in Chicago's annual St. Patrick’s Day river-dyeing event, was selected as it is harmless and quickly degrades into the environment. But why, you may ask, did Save Windermere and Windrush Against Sewage Pollution introduce dye into Cunsey Beck?
The Background
Near Sawrey WwTW Outfall
The story begins on June 21, 2022, when a devastating Category 1 fish kill was reported in the heart of the Lake District National Park. The EA stated that “100% of life within the river had been killed,” including rare and protected species of international importance. Despite this, the EA failed to conduct an adequate investigation or request all relevant evidence from United Utilities—who, in our opinion, are the main suspect in this catastrophe. For a detailed breakdown and to understand why we have called for a public inquiry into the EA’s failing, see our full report here.
Our focus today isn’t the fish kill itself but the EA’s only response to this disaster: installing water-quality monitors, known as sondes, in Cunsey Beck.
The EA’s Response
Following the fish kill, the EA stated:
“We understand the concerns that local people have about water quality and how frustrating it is not to have clear answers about what has caused some of the incidents we have seen. Installing ‘sondes’ will enable us to have access to better information than ever before, helping us take prompt action to maintain and improve water quality in Cunsey Beck. The ‘sondes’ will also help us better understand the complex issues facing Windermere and secure the future of this iconic lake for generations to come.”
They further claimed that, over the next year, their agenda would include monitoring trends and pollution hotspots, focusing on reducing pollution sources, and regularly reviewing their findings.
A sonde is a piece of equipment that monitors water quality by measuring parameters like temperature, pH, conductivity, and dissolved oxygen. Sondes can be left in place for extended periods of time and programmed to take measurements at regular intervals. The data collected is then stored and transmitted to a data logger or other device for analysis. On Cunsey Beck, this data can be viewed almost real-time.
So, where did the EA place the sondes on Cunsey Beck to monitor the single point source of pollution in the river? One was installed immediately upstream of Near Sawrey Wastewater Treatment Works (WwTW), while the second was positioned about a kilometre downstream from the sole point source of pollution on Cunsey Beck.
Our Concerns with the Placement
From the outset, Save Windermere voiced concerns about the sondes' locations. On April 20, 2023, we challenged the EA’s setup:
“The sonde system in place sits below Out Dubs Tarn, about 1 km downstream of this point source of pollution. Why is that? There is only one point source of pollution between where the first sonde is and the second, and this site may be impacting the river. Is this not yet another reason to position the second sonde closer to the point source?”
In response, the EA repositioned the downstream sonde—but once again, it was poorly placed, this time in a stagnant section of the river. On May 5, 2023, we flagged this issue:
“The downstream sonde doesn’t seem to be in the main flow of the river. Will this affect the accuracy of the results? I have attached a video showing the sonde’s current placement, but it appears to be in a sheltered area, which raises concerns about how this will impact the data, especially if there’s any discharge from Near Sawrey WwTW.”
After persistent pressure, the EA once again relocated the sonde to within 40 metres of the sewage pipe. At first, this seemed like progress. However, during a site visit with Ashley Smith, the founder of Windrush Against Sewage Pollution and a retired detective superintendent, we noticed a critical oversight. While watching the river, he pointed out that the flow passing the sewage pipe would never actually move past the sonde, as it had been placed on the wrong side of the river.
To confirm this, we introduced the fluorescein dye at the sewage outfall. As suspected, the dye didn’t pass the sonde at all. This means any sewage spills from Near Sawrey—a prime suspect in the fish kill and the main cause for concern on Cunsey Beck—would go undetected by the EA’s monitor.
The Bigger Picture
The EA’s only tangible action following its failure to investigate the fish kill in Cunsey Beck has proven ineffective and continues to let the polluter off the hook. Worse still, it raises questions about whether these decisions deliberately protect United Utilities rather than the environment.
This isn’t just a Windermere issue—it’s a national one. Across the UK, in-river monitors are failing to capture the true impact of point-source pollution, which remains variable, unreliable, and susceptible to manipulation. Save Windermere has long called for real-time monitoring of sewage discharges before they enter our waterways. The technology exists. The will to implement it, it seems, does not. This case clearly illustrates how pollution is slipping through the cracks, and how the current system is skewed to benefit the very companies it is meant to regulate. Addressing these issues and monitoring the impact of these sites on our freshwater environment should be incredibly straightforward.
What Needs to Happen Next?
We are calling for an immediate intervention from Secretary of State Steve Reed and Water Minister Emma Hardy to implement real-time sewage monitoring in Windermere. This monitoring must not only track when spills occur, but also the flow/volume being released into the environment, as well as providing real-time sewage quality data, including phosphorus, ammonia, pH, turbidity, nitrate, and dissolved oxygen levels.
Windermere should serve as a test case for this intervention, demonstrating why the expense of installing such devices is crucial—not only for holding the water companies accountable, but also for accurately assessing the environmental damage being caused. The current system is failing—allowing pollution to go unnoticed and unchecked. It’s time for meaningful action that delivers for Windermere.
