Before You Take the Plunge: The Hidden Dangers of Open-Water Swimming
Open-water swimming has become increasingly popular, offering people a chance to enjoy nature, exercise outdoors and escape the restrictions of traditional swimming pools. Rivers, lakes, harbours and other freshwater locations can look inviting, particularly during warm weather. However, recent research and reported illnesses have highlighted that apparently clean water can still contain microorganisms capable of causing illness.
A recent report highlighted concerns after two children were hospitalised following contact with water at Christchurch Harbour in Bournemouth during an E. coli outbreak. A woman was also reported to have become seriously unwell after being exposed to the same area. The incidents have renewed attention on the potential health risks associated with recreational water.
Freshwater may contain hidden health risks
Water can appear clear and safe while still containing microorganisms that cannot be seen with the naked eye. According to research from the University of East Anglia, contamination at freshwater recreational sites may be associated with illnesses affecting swimmers.
The research analysed information from 2,368 people in Hungary. Participants were assigned either to swim for 10 minutes, including several full immersions of the head, or to remain on shore. The swimming took place at four freshwater bathing sites.
The findings suggested that swimmers were more than twice as likely to experience certain skin problems, including rashes, ulcers and itching, compared with people who did not enter the water. Importantly, the study also found a connection between increasing levels of E. coli and a higher likelihood of gastrointestinal illness.
What can cause illness?
Freshwater can contain a mixture of microorganisms and other contaminants. Some can enter waterways through faecal pollution, while others occur naturally in the environment.
The research found that for every tenfold increase in E. coli concentration, the risk of gastrointestinal illness increased by approximately 73 per cent. Higher concentrations of somatic coliphages, viruses that infect bacteria, were also associated with increased illness risk.
These findings are significant because E. coli can indicate the presence of faecal contamination. Such contamination can introduce other organisms capable of causing gastrointestinal illness.
Potential illnesses associated with open-water exposure include stomach infections, respiratory infections, skin problems, and ear or eye infections. Microorganisms mentioned in the supplied source include norovirus, giardia and cryptosporidium. In many cases, illness is expected to be mild and short lived, but more serious infections can occur.
Skin problems can have different causes
One of the notable findings was that skin complaints among swimmers were not necessarily linked to levels of faecal contamination.
Researchers suggested that naturally occurring organisms could be responsible for some of these problems. One possibility is cercarial dermatitis, commonly called swimmer's itch. It is associated with parasites released by waterfowl. These parasites can come into contact with human skin and cause an itchy rash.
This means that even water without obvious signs of sewage contamination may not be completely free of organisms capable of affecting the skin.
Rainfall can change water quality
Weather conditions can also influence the quality of recreational water. Heavy rainfall can wash bacteria and other contaminants from agricultural land, urban areas and sewage systems into rivers, lakes, coastal waters and other bathing locations.
As a result, water quality can change following periods of significant rainfall. A location that appeared suitable for swimming previously may therefore have a different level of contamination after a major weather event.
This is particularly relevant for people who regularly participate in open-water swimming, paddleboarding, rowing or other activities that involve direct contact with natural water.
Blue-green algae is another concern
Freshwater users should also be aware of blue-green algae, particularly when blooms or scum are visible.
According to the information supplied in the source, contact with freshwater blue-green algae can cause symptoms including skin rashes, irritated eyes, vomiting, diarrhoea, fever and muscle or joint pain. Some blooms can produce toxins that are dangerous to animals and may cause severe illness.
However, not every blue-green algae bloom is necessarily toxic, and appearance alone cannot reliably determine whether a bloom is harmful.
For this reason, people should take official water-quality warnings seriously rather than relying only on how clear or attractive the water looks.
Who may face greater risks?
Anyone entering open water can potentially become ill because natural bodies of water contain microorganisms. However, the source identifies several factors that may increase the likelihood of illness.
Children and inexperienced swimmers may be more likely to swallow water accidentally. People with weakened immune systems can also be more vulnerable to infections. The source additionally notes that swimming in rivers and estuaries may carry greater risks, while rainfall can influence contamination levels.
Cuts and broken skin may also be an important consideration when taking part in water activities. One of the children mentioned in the report had been paddleboarding with a cut on their foot when exposed to the harbour water.
Does this mean people should stop swimming outdoors?
Not necessarily. The research does not suggest that every open-water swim will result in illness.
Professor Paul Hunter, who led the analysis, noted that the overall rates of illness were relatively low. The study found that just over two per cent of participants developed gastrointestinal illness, with a similar proportion experiencing skin problems. Respiratory, ear and eye infections were uncommon.
The important message is therefore about awareness and risk management rather than automatically avoiding every natural swimming location.
People considering open-water activities should check available water-quality information and follow local warnings. Avoiding water after pollution incidents or when official authorities advise against swimming can reduce unnecessary exposure. It is also sensible to avoid swallowing untreated recreational water and to take particular care when swimming with children.
Why water monitoring matters
The research reinforces the importance of monitoring microorganisms in recreational water.
The scientists concluded that higher levels of E. coli and related indicators were associated with greater risks of gastrointestinal illness. The findings also raised questions about whether different indicators and standards may be needed for freshwater and coastal environments because microorganisms can behave differently in these settings.
Meanwhile, authorities were investigating the reported pollution incident at Christchurch Harbour. The Environment Agency said its officers were taking samples and examining the performance of water company assets following the reported incident.
For swimmers and other water users, such monitoring provides an important layer of protection. It can help identify potential contamination and communicate risks to the public.
The bottom line
Natural swimming can be enjoyable and beneficial, but clear-looking water should not automatically be assumed to be risk-free. Rivers, lakes and harbours can contain bacteria, viruses, parasites and other contaminants that may cause stomach problems, skin reactions or other infections.
The recent research suggests that contamination levels can influence gastrointestinal illness, while some skin problems may arise from naturally occurring organisms. Rainfall, pollution events and environmental conditions can also affect water quality.
The safest approach is to stay informed, pay attention to official warnings and avoid entering water when authorities advise against it. Extra caution is appropriate for children, inexperienced swimmers and anyone who may be particularly vulnerable to infection.
Open-water swimming does not have to be avoided altogether, but understanding the potential hazards can help people make better-informed decisions before taking the plunge.
Sources
- University of East Anglia research as reported in the supplied source material.
- UK Health Security Agency, Swim Healthy guidance, as cited in the supplied source.
- Environment Agency comments regarding sampling and investigation of the reported Christchurch Harbour pollution incident.
Disclaimer
This article is for general informational purposes only. It is not medical advice and should not be used to diagnose, treat or prevent an illness. Water conditions can change quickly, and readers should follow current guidance from relevant public-health, environmental and local authorities. Anyone who becomes seriously unwell after exposure to recreational water should seek appropriate medical advice.