When the Water Isn’t as Clean as It Looks
One of the most magical things about wild swimming is the sense of freedom it brings — plunging into a glittering lake, a chalk stream, or a wave-lashed cove feels about as far from everyday life as you can get. But beneath that sparkling surface, invisible threats can sometimes lurk. Elevated bacteria levels in open water are a genuine concern for swimmers around the world, and the UK is no exception.
Reports of popular swimming spots being temporarily closed due to high bacterial contamination are becoming more common, and while it can be frustrating to arrive at your favourite spot and find it off-limits, those advisories exist for very good reason. Understanding why bacteria levels rise, what the risks are, and how you can take steps to protect yourself is essential knowledge for any enthusiastic wild swimmer.
What Causes Bacterial Contamination in Open Water?
Bacterial contamination in rivers, lakes, and coastal waters can come from a surprising range of sources. It’s rarely a simple story, and the levels can fluctuate dramatically depending on conditions.
Agricultural Runoff
One of the most significant contributors in rural areas is agricultural runoff. When it rains heavily, water picks up animal waste from fields and carries it into nearby watercourses. This can introduce harmful bacteria such as E. coli and Campylobacter into rivers and lakes almost overnight. Many UK wild swimming spots sit downstream from farmland, making this a particularly relevant concern here.
Sewage Overflow
Combined sewer overflows (CSOs) have been a hot topic in the UK in recent years, and for good reason. During periods of heavy rainfall, our ageing sewage infrastructure can become overwhelmed, leading to untreated or partially treated sewage being discharged directly into rivers and coastal waters. This is a significant source of bacterial contamination and one that has prompted widespread campaigning from wild swimmers and environmental groups alike.
Wildlife and Natural Sources
It’s worth noting that not all bacterial contamination is human-caused. Waterfowl, deer, and other wildlife naturally deposit waste into and around water bodies. In heavily populated wildlife areas, this alone can push bacteria counts to levels that warrant caution, particularly in warm, still water where bacteria thrive.
Warm Weather and Low Flow
Bacteria multiply rapidly in warm conditions. During hot spells, particularly when water levels are low and flow is slow, contamination that might otherwise be diluted can become concentrated. This is why summer — the peak season for wild swimming — can also be a peak period for water quality issues.
What Are the Health Risks?
Swallowing contaminated water, or even getting it in your eyes, nose, or ears, can lead to a range of unpleasant illnesses. The most common include:
- Gastroenteritis — stomach cramps, nausea, vomiting, and diarrhoea
- Ear infections — particularly common in frequent swimmers
- Eye and skin irritation
- Respiratory infections — especially if water is accidentally inhaled
In most cases, healthy adults will recover within a few days, but the very young, elderly, pregnant women, and those with compromised immune systems face greater risks. It’s always worth being extra cautious if you fall into any of these categories.
How to Swim More Safely in Open Water
The good news is that with a little preparation and awareness, you can significantly reduce your risk and keep enjoying the wild swimming you love.
Check Official Water Quality Data
The Environment Agency publishes bathing water quality data for designated sites across England, and similar data is available in Scotland, Wales, and Northern Ireland. These are a good starting point, but be aware that designated bathing sites are only a fraction of the places where people actually swim.
Avoid Swimming After Heavy Rain
This is arguably the single most effective rule of thumb for wild swimmers. Rainfall dramatically increases the risk of both agricultural runoff and sewage overflow, so waiting 48 to 72 hours after significant rainfall before entering the water is a sensible precaution at most spots.
Test the Water Yourself
This is where you can really take control of your own safety. Rather than relying solely on official data — which can be infrequent or unavailable for non-designated spots — you can test the water quality yourself before you swim. Water quality test kits designed for wild swimmers make it easy to check for indicators of bacterial contamination at your chosen spot, giving you real-time information and genuine peace of mind.
If you regularly swim at the same location, testing periodically also helps you build up a picture of how water quality changes with the seasons, rainfall, and other factors — knowledge that makes you a much more informed and safer swimmer.
Be Part of the Solution
Wild swimmers are increasingly at the forefront of campaigning for cleaner waterways in the UK. By testing water quality at your local spots and sharing that data with community groups, local authorities, or citizen science projects, you contribute to a broader understanding of the problem and add pressure on those responsible to act.
Knowledge is power — and in this case, it’s also protection.
Ready to Swim Smarter?
Don’t leave your safety to chance. Whether you’re a seasoned open-water swimmer or just discovering the joy of wild dipping, having the right tools to assess water quality is a brilliant investment. Browse our range of easy-to-use water quality test kits at wildswimmingtests.co.uk/shop and take the first step towards swimming with real confidence — wherever the water takes you.
📷 Photo by Jaz Blakeston-Petch on Unsplash
