Going swimming? 10 easy ways to reduce your risk of getting ill

Kate Rew, Tom Kay and others on a microadventure

Fear and media headlines about water quality are running high in the UK, but when we researched OSS members in 2022 they logged 1.85 million swims between them all around the world and 207 incidents of sickness that they attributed to water quality. That’s one incidence of sickness for every 9,094 swims.

As the largest organisms in the water, and only briefly in there (compared to a dragonfly nymph for example, that might be there for up to 5 years), we are remarkably robust to less than pure water. 80% of swimmers had never been sick, 10% reported one occasion of feeling ‘a bit iffy’, and a further 10% reported being sick one to four times (within the context of having taken 1434 swims each on average). 

If you are worried about water quality where you swim, it may give confidence to know that there are things we can do to reduce our risk of sickness other than – perish the thought, give up swimming (or not take it up in the first place. We are so sad to see people scared off starting swimming). Nothing is without risk, and outdoor swimming is full of risks, such as moving water, cold, and weather. Possible issues with water quality is just one one of many risk factors that you can learn to moderate, and balance against the positives – 94% of those surveyed swim for joy, 84% cherish the immersion in nature, 82% like the freedom and flexibility of the sport and 68% like the benefit of physical fitness.

Kate Rew


  1. Don’t go in if it looks iffy
  2. Caution after heavy rain
  3. Consider the location – head for purer water
  4. Don’t swallow water
  5. Know your body/current state of health
  6. No contact lenses
  7. Cover cuts/allow major wounds to heal
  8. Dry your ears
  9. Wash your hands


So with better water quality high on the political and personal agendas, here’s what I and many other swimmers do to reduce risk of illness swimming.  What we don’t do, that often, is stop swimming.

Every body of water is different – use these tips and the features below to get to know yours.

  1. Do a sight and smell test: you can tell a lot about water just by looking at it, or being conscious of any bad odours. If it looks iffy and unappealing, consider going somewhere else or waiting for another day. Look for things like floating pollutants, blue-green algal blooms on the surface, or an oily sheen on the water. If you’re not sure: another option is to do head up breaststroke.
  2. Don’t drink the water – and do weatherproof your stroke. Stomach infections will not make their way into your body via osmosis, you actually need to swallow water – which most swimmers don’t (chances of infection via the mucous membranes of the nose and mouth are very slim). If swimming front crawl, learn to breathe on both sides so that you can breathe away from chop if you are swimming in windy conditions. Practise swimming in chop without taking water on board. Both of these skills grow in importance for those doing swim events or challenges, where the distance and direction are set and can’t be changed to avoid any weather on the day – if it’s just for yourself, you can choose to swim in millpond weather, but if you’re training for something specific it pays to be ready for whatever greets you.
  3. Wash your hands before eating after a swim – including after handling gear. 
  4. Cover small cuts with waterproof plasters before entering the water. This will help protect you from Weil’s disease, and from bacteria associated with animal poo which can come from the banks. Wash the cuts after swimming and replace plasters with new ones. (For serious wounds, deep cuts and post-surgery openings ask your medical professional about healing times).
  5. Be cautious after heavy rain, which carries pollution into the water. Rain washes whatever is on the surface of a field, land, roads and driveways off and into the river, or into drains and then the river.. and then into lakes, and into the sea. So after a big downpour this ‘runoff’ will have carried any pollution (including fertiliser) into the river, and then lakes and the sea. This is a rural and urban phenomenon and many swimmers stay out of their rivers at points because of rain. Heavy rain can also lead to sewage overflows, some of which you can track. (See end). Swimmers often get to know their patch, becoming aware of what industry and agriculture is present in the catchment of the water body.
  6. Consider opting for head up breaststroke or sidestroke if concerned about bathing water quality.
  7. Only you can know your own resilience. The strength of your immune system and general wellbeing can be big factors in your susceptibility to bugs you may encounter – and your ability to fight them off.  Some of us never get stomach infections, others get them all. Hangovers, stress, being tired, being recently ill, getting cold, and doing endurance sport will all lower your immunity. High profile cases of swimmers who get sick doing challenges often tick all these boxes: undertaking a challenge based on a PR not weather-based schedule (i.e. can’t change swimming days if there’s a storm), swimming for long distances, getting seriously cold, and wearing down their immunity. Charity challenges that ask you to swim every day regardless of conditions carry the same risk.
  8. Do not swim in contact lenses, which work like petri dishes to multiply bacteria, trapped between them and the eye (warm and moist, ideal conditions). If you do: make them disposable and dispose of them afterwards (even if you use goggles). Prescription goggles are available.
  9. To reduce the risk of swimmers’ ear, keep your ears as dry as possible. Use a swim hat, swim hood, ear plugs, or custom-fitted swim moulds when swimming, and use swimmers ear drops and a towel to dry your ears thoroughly after swimming. Don’t remove ear wax – which may help protect your ears from infection. Avoid causes of abrasion to the inner-ear, particularly when drying.
  10. Think about where your swim is and what is happening upstream and immediately surrounding the area: highland rivers and streams that have not been manhandled are going to have purer water than rivers that have made their way through and under cities and towns. Water treatment works are visible on ordnance survey and google maps and you may wish to swim upstream rather than immediately downstream of them (particularly after heavy rain). Be aware not all water treatment works have combined sewage overflows or discharge untreated sewage (despite the media noise).

If you swim and suffer skin rashes, eye irritation, vomiting, diarrhoea, fever or cold like symptoms and muscle and joint pain go to your doctor or A&E and mention you have swum in an outdoor water body recently. With both Weil’s Disease and Blue Green Algae quick treatment is recommended. Weil’s Disease can take a few weeks to show. See links for further information.

Kate Rew is the author of The Outdoor Swimmers’ Handbook (Rider), which contains more information on Planning a Swim. Available widely internationally and signed in The OSS Shop.


Kate Rew  (@kate_rew)