Wild swimming can expose you to many bacteria and viruses – here’s how to keep yourself safe

Wild swimming is becoming an increasingly popular pastime in the UK – especially in the summer when temperatures soar. With the recent news that 27 new wild swimming spots have been designated bathing waters in England, many more may be thinking of giving this hobby a try.

But with Environment Agency reports revealing nearly 4 million hours of raw sewage were discharged into England’s rivers and coastal waters last year – nearly double the number of spills reported in 2022 – many may be wondering if it’s still safe to swim, even in these designated spots.

Raw sewage can contain a variety of germs that can seriously harm our health.

Some examples are Escherichia coli (which most of us know better as E coli), which can cause both gastrointestinal and urinary infections. Some of the serious symptoms it can cause include severe diarrhoea, stomach cramps, vomiting and pain during urination. It can also cause ear infections.

This type of bacteria is one of the most prevalent waterborne pathogens in English waterways, and has even been found in several wild swimming sites.

Infections with Salmonella enterica, Shigella flexneri, Vibrio cholerae and Campylobacter jejuni – all of which can also be found in wastewater – can cause similar symptoms as E coli.

Weil’s disease (leptospirosis) is another bacterial infection that can be picked up from sewers, rivers, ponds and canals that are contaminated with rat urine. Most people who catch Weil’s disease will have no symptoms – or will only experience mild flu-like symptoms. But some people get seriously ill, developing a fever, body pain, nausea, diarrhoea and jaundice (yellowing of the eyes and skin). Dogs can also get ill from leptospirosis by drinking or bathing in contaminated waters.

Several viruses can also be spread through wastewater. Norovirus and astrovirus, for instance, both cause diarrhoea and vomiting. These can also be spread in swimming pools.

Hepatitis A can be spread in wastewater as well. This can lead to life-threatening liver disease if not treated promptly. Fortunately, the chances of catching hep A from a wild swim are quite low – unless you ingest a lot of water.

Many of the microbes in sewage water might be resistant to antibiotics, as they might have been exposed to these drugs before. antibiotics used to treat both humans or animals. This means that infections caused by these bacteria may be more difficult to treat.

Sewage also often contains high levels of toxic heavy metals, such as cadmium, lead and mercury. These can lead to serious poisoning or even cancer in rare cases if ingested in high levels.

Pesticides can also be in river waters, especially when farmlands become flooded. Symptoms linked to pesticide poisoning range from immediate short-term effects (headaches, dizziness, muscle twitching, weakness, tingling sensations, nausea) to more serious effects after long exposure (more than 24 hours) or at high levels of exposure – including birth defects, learning disabilities, behavioural changes, organ damage, cancer, brain tumours and asthma.

Safe swimming

When someone is swimming, contaminated water can enter the body through the ears, eyes, nose, mouth and urinary tract. Infections can also sometimes enter through the skin if someone has a wound, cut or abscess.

The dose of the infectious agent (the number of bacterial cells or viral particles) is also an important factor in whether a person gets sick from wild swimming or not. The dose depends both on the “microbial load” of the wastewater (microbial cells per millilitre) and the amount of water swallowed by the swimmer.

For example, Salmonella needs about a 50,000 cells to cause disease – but Streptococcus only need 200 cells.

Different microbial strains have different infectious capacity, so it’s not always easy to predict the severity of a waterborne illness. Some strains of E coli, for instance, are more virulent than others with only ten to 100 cells needed to cause infection.

Although wild swimming may come with risks, there are many things you can do to protect yourself and avoid illness.

First, only swim in areas that have been officially designated as “bathing waters”. These will be routinely tested by the Department for Environment, Food and Rural Affairs throughout the bathing water season (between May and September) to monitor levels of both microbial and chemical contaminants and ensure waters are of suitable quality for swimming.

There are several online tools you can check to know whether a specific location is suitable for swimming – such as Swimfo and the Rivers Trust Sewage Map.

When wild swimming, protect yourself by wearing earplugs and goggles. This will help prevent you from getting ear and eye infections if exposed to contaminated waters. Avoid swallowing water when you swim. By staying informed and taking necessary precautions, you can still enjoy a refreshing wild swim.

Georgios Efthimiou does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.