It looked, at first, like another one of those pollution alerts that have become all too familiar to people living along the Cornish coast. A warning appeared on South West Water’s live map, showing an apparent sewage discharge at Flushing Pumping Station, a site that sits close to the water and not far from the busy harbour towns of Falmouth and Penryn. The alert claimed that a discharge had taken place within the previous 48 hours, with the event logged as beginning at 5.31 pm on Thursday, August 13, and ending at 6.44 pm the same evening. For anyone who saw that warning, it was a worrying sight. We have become conditioned, rightly, to be suspicious of sewage spills in our rivers and seas. But South West Water has now clarified that this particular alert was not what it seemed. The company says the activation was caused by very high spring tides in the area, not by an actual release of sewage. In fact, the utility has been keen to stress that nothing was released at all. It was, in their words, a false activation recorded by monitoring equipment that was fooled by the extraordinary tidal conditions. The company also confirmed that every asset in the area had been checked and was operating as expected, which is reassuring in itself. But the incident raises a broader question that matters to everyone who cares about clean water: how do we know what is real and what is a false alarm when the warnings appear, and how can we trust the systems we rely on to tell us the truth about what is happening beneath the surface?
For the people who live in Flushing, and for all the swimmers, sailors, paddleboarders and beach walkers who use the nearby Fal estuary, this is more than just a technical issue. It is about peace of mind. When you see a sewage discharge alert on a map, your immediate reaction is not to wonder about the inner workings of an Event Duration Monitor or to consider whether the tides might have interfered with the equipment. Your reaction is much more instinctive. You imagine the water turning murky, you cancel your plans, you worry about the children who were splashing in the shallows an hour before, and you feel that familiar mix of anger and sadness that we have allowed our natural waters to be treated so carelessly. That is why South West Water’s clarification matters. The company has acknowledged that the alert was alarming and has tried to explain, in plain language, that the sensors were tricked by the spring tides. Spring tides, as many people know, happen around the new moon and the full moon, bringing especially high high-tides and particularly low low-tides. During these periods, seawater can push into places it would not normally reach, including the chambers and pipes where monitoring equipment is housed. Sometimes the water moves with great force; sometimes it simply sits there, confusing the delicate electronic instruments that are supposed to tell us whether an overflow is active. The result is a recorded event that looks, on a map, exactly like a sewage spill, but is in fact nothing more than a natural phenomenon playing tricks on a machine.
To understand how this can happen, it helps to understand what these monitors are actually for. South West Water’s Event Duration Monitors, known as EDMs, are not designed to measure the volume of wastewater that might be released. They do not test the contents of the water. They are not chemical sensors or biological detectors. Instead, they are simple devices that indicate when a combined sewer overflow may have been active, and for how long. In many parts of the country, the same pipes that carry sewage from homes and businesses also carry rainwater from streets and roofs. During heavy rain, the combined volume can sometimes exceed the capacity of the treatment works. To protect homes and streets from flooding, these systems are designed to overflow at certain points, usually into rivers or the sea. The EDMs are there to monitor those overflows and to provide data that can be used by regulators, environmental groups and the public. But they are not perfect. They are not able to tell the difference between an actual overflow and the many ordinary, harmless things that can occur in a pipe full of water. A small piece of wood, a clump of leaves, a spider web, a few bubbles, a patch of foam, or even a sudden surge of water caused by an exceptionally high tide can be enough to trigger the device. In other words, the monitor does what it is told to do: it detects a possible sign of activity and records it. But the interpretation of that activity is left to humans, and that interpretation takes time.
That delay between detection and interpretation is at the heart of the confusion that surrounded this week’s alert. South West Water has explained that its online map displays near-real-time information received from monitors before an investigation has established the reason for an activation. This means that when you look at the map, you are seeing raw, unverified data. In most cases, that is a good thing. It is better to know about a possible spill immediately and to be cautious than to be kept in the dark for days while the company quietly investigates. But the downside is that false readings appear on the map as if they were real events, which is exactly what happened at Flushing. The alert was visible to anyone who looked at the live map, and it remained visible long enough for people to screenshot it, share it on social media, or report it to local environment groups. South West Water says that confirmed false readings are removed from the published data, which is reassuring. But by the time those false readings are removed, the damage to public trust may already have been done. People may have already changed their plans, worried about their health, or added yet another data point to their mental catalogue of environmental failures. And because the data is shared with third parties, the story does not always end when the water company updates its own systems.
Indeed, the alert at Flushing remained visible on the Surfers Against Sewage sewage map, a popular online tool used by thousands of people to check water quality before going into the sea. Surfers Against Sewage, an environmental charity, presents information received from water-company monitoring systems and retains that data online for 48 hours. This is incredibly valuable work, and it has helped to shine a light on the scale of sewage pollution in our rivers and seas. But it also means that raw, unverified alerts from water companies can take on a life of their own. Even after South West Water confirmed that the Flushing activation was a false reading caused by high spring tides, the warning could still be seen on the charity’s map, simply because the data had been received and retained according to its own rules. This is not the fault of Surfers Against Sewage. It is a sign of how complicated it can be to communicate environmental information accurately in real time. It also shows how important it is for water companies to be more careful about how they present their data, and for them to explain, clearly and quickly, whenever an alert appears to be false. The public should not have to become amateur hydrologists or to guess whether a red marker on a map means danger or simply a technical glitch. We should be able to trust that the information we are given is as reliable as possible, and when it is not, we should be told that openly and without delay.
At its heart, this story is about the delicate relationship between technology, nature and public trust. South West Water has done the right thing by speaking out quickly and explaining what happened at Flushing Pumping Station. The company has said that the alert was not an actual discharge, that the high spring tides caused the recording equipment to give a false activation, and that all assets in the area have been checked and are operating as expected. That is genuinely reassuring. It is also a reminder that our water infrastructure is monitored, maintained and scrutinised in ways that would have been unthinkable a generation ago. But it is equally a reminder that the systems we rely on are not infallible. Sensors can be fooled. Data can be misunderstood. Alerts can spark panic before the truth is known. For those who live in Flushing, the news will no doubt come as a relief. For everyone else, it is a valuable lesson. We need to hold water companies to account for the very real problem of sewage spills, but we also need to be careful not to jump to conclusions every time a red dot appears on a map. The truth matters. And in this case, the truth is that the water was safe, the station was working as it should, and the alarm was the result of the sea doing what the sea does at high tide, surprising us and reminding us that we do not control as much as we might like to think. Yet the episode also shows that communication matters just as much as engineering. A false alarm, properly explained, can build trust. Unexplained, it can destroy it. With more high tides and changing weather on the horizon, we all need answers that are quick, honest and above all, human.