When ‘Excellent’ Isn’t Enough
For most wild swimmers, spotting an ‘Excellent’ water quality rating at a favourite swim spot feels like a green light. It suggests the water has been tested, assessed, and deemed safe. But what if those official ratings are only giving us part of the picture? What if the bugs that make swimmers genuinely ill aren’t the ones being measured?
This is a question that more people in the wild swimming community are starting to ask — and it’s one worth exploring carefully. Understanding what official water testing actually measures, and what it doesn’t, could be the difference between a fantastic swim and a trip to A&E.
What Do Official Water Quality Tests Actually Measure?
In the UK, bathing water quality is assessed by the Environment Agency in England, and equivalent bodies in Scotland, Wales, and Northern Ireland. Their testing primarily looks for two types of indicator bacteria:
- Escherichia coli (E. coli) — a bacterium found in the gut of warm-blooded animals, used as an indicator of faecal contamination
- Intestinal enterococci — another group of bacteria associated with sewage and animal waste
These are called indicator organisms. The idea is that if these bacteria are present in high numbers, it suggests other harmful pathogens may also be present. If their levels are low, the water is considered safe.
It’s a logical approach — but it has significant limitations.
The Pathogens That Don’t Show Up in Standard Tests
The problem is that nature’s aquatic hazards go well beyond E. coli and enterococci. There are several other organisms that can cause serious illness in swimmers yet won’t be flagged by standard bathing water assessments:
Harmful Algal Blooms (Cyanobacteria)
Blue-green algae, which is actually a type of cyanobacteria rather than true algae, can produce powerful toxins capable of causing liver damage, neurological symptoms, and severe skin irritation. These blooms can appear even in water that scores ‘Excellent’ for bacterial contamination, particularly during warm, still summer conditions.
Cryptosporidium and Giardia
These microscopic parasites are shed in the faeces of infected animals and humans. Crucially, they are highly resistant to chlorine and are not reliably detected by standard indicator bacteria tests. Ingesting even a tiny amount of contaminated water can cause prolonged gastrointestinal illness lasting days or weeks.
Leptospira (Weil’s Disease)
Spread through the urine of infected animals — particularly rats — Leptospira bacteria cause leptospirosis, sometimes known as Weil’s disease. In severe cases, it can lead to kidney failure and is potentially life-threatening. Standard bathing water tests do not screen for it.
Viruses
Norovirus, hepatitis A, and other enteric viruses can all be present in water affected by sewage, yet current UK bathing water standards do not routinely test for viral contamination. Research suggests that viral risks may be underestimated in official assessments.
Why the Ratings System Has Gaps
Official ratings are based on samples taken at designated bathing waters — and only during the official bathing season, which typically runs from mid-May to the end of September. Many wild swimmers take to the water outside this window, when no active monitoring is taking place at all.
Sampling is also periodic rather than continuous, meaning a single pollution event — a sewage overflow after heavy rain, for example — may occur between sample dates and go entirely unrecorded. Water conditions can change dramatically within hours, and a clean result from last Tuesday tells you very little about what’s in the river on Saturday morning.
Furthermore, the vast majority of wild swimming locations — rivers, lakes, reservoirs, coastal coves — are not designated bathing waters at all. They receive no official monitoring whatsoever.
What Can You Do to Swim More Safely?
None of this is meant to put you off wild swimming — far from it. The mental and physical benefits are well documented, and millions of people swim in UK waters every year without incident. But going in with eyes open is the sensible approach.
- Avoid swimming after heavy rainfall, when sewage overflows and agricultural runoff are far more likely
- Cover any cuts or wounds before entering the water, and shower promptly afterwards
- Never swallow water — keep your mouth closed when submerging
- Learn to identify blue-green algae visually, and avoid any water that looks pea-green, scummy, or has a paint-like surface
- Test the water yourself — especially at locations with no official monitoring
This last point is increasingly important. Personal water quality testing kits allow swimmers to check for key indicators of contamination before they get in. While no home test can replicate a full laboratory panel, even a basic E. coli or coliform test provides a meaningful data point that official ratings may not.
Take Your Safety Into Your Own Hands
The wild swimming community is growing fast, and with it comes a growing awareness that official reassurances don’t always reflect the full picture. Being an informed, proactive swimmer means not relying solely on seasonal ratings from a government website.
If you regularly swim at locations without official monitoring — or you simply want greater peace of mind before every dip — explore our range of water quality test kits at wildswimmingtests.co.uk/shop. Designed with wild swimmers in mind, they’re a practical, affordable way to add an extra layer of safety to every swim.
Stay curious, stay informed, and stay safe out there.
📷 Photo by Mario La Pergola on Unsplash
