Swimrun Health Dangers on Land and Water

It’s time!

The season and the training kicks in. Take care out there and don’t forget about all the dangers!

/The Wos Team

*Originally posted in 2016*

Swimrun is a sport that has great health benefits, there can be no doubt about it. Swimming and running outdoors ensures you get a full body workout whilst filling up your reserves of vitamin D from the sun. Changing between swimming and running is great for not overstraining muscles and running and swimming on uneven terrain and in open water engages far more important core muscles than in a static controlled environment. So you might wonder why we should take some of the fun out of it by bringing up rare dangers that are unlikely to affect you. Well, simply because by being aware of these dangers and the necessary precautionary measures might help you avoid the risks altogether and let you head out knowing you will be at minimal risk of serious consequences.To start with, the most obvious dangers are injuries from falling or hitting objects (branches, rocks, etc.) as well as overheating for running and hypothermia and drowning for swimming. As we are quite sure that you have figured that out yourself and know that the best prevention is running and swimming with a buddy that can watch out for symptoms, call for help and give first aid, we won’t focus on that. Instead, we will bring attention to less obvious threats found on land and in water. With the exception of the Loch Ness monster that the organizers warned us for in the Loch gu Loch race a couple of weekends ago, these creatures tend to be very small indeed. As you will have guessed by now we are talking about bugs, parasites, viruses and bacteria. And although the risks are small there are quite a few accounts of outbreaks related to races. A quick review of the scientific literature identified outbreaks in mud obstacle races and muddy mountain bike races caused by the bacteria campylobacter, outbreaks in triathlon events caused by leptospirosis and a mass river swim event outbreak caused by norovirus. Cases are likely to have occurred in many other races as well, but will not have been reported or written as a scientific publication. Considering that the numbers of swimrun races are increasing and since they are now held in many different kinds of environments fresh water/brackish/saltwater, close to cities, near farmland or in isolated places etc. this information becomes even more relevant. Further down we have listed some relevant dangers from microbes, algae and jellyfish found in temperate climates and what you can do to avoid them. In short, to protect yourself:

  • make sure you have your vaccinations up to date
  • do not swim with open wounds
  • use earplugs and goggles
  • if you get ticks, remove them as soon as possible
  • if you get feverish or get gastrointestinal symptoms within some days to weeks after a race have it checked out by a doctor and do not forget to mention that you have participated in a Swimrun so that the doctor tests you for the right pathogens.

We are not bothering telling you to avoid to swallow water during the swims and clean your hands before handling food… We know it is impossible.

As for race organizers, we want to bring these dangers to their attention so that they will consider the quality of the water when planning races. They should also be aware that otherwise clean waters may become contaminated after heavy rains and flooding. At the time of the race it is a good idea to inform participants about local dangers such as jellyfish, ticks and algal bloom.

Threats on land

The number of threats from disease listed here may be fewer on land than in water, but the disease threat from ticks is real and the diseases they transmit can cause serious illness. Ticks are not found everywhere and most ticks do not carry disease even in areas where the diseases can be found, but many Swimrun events are held in areas where you are at risk. Although even those who are unlucky and get infected by the diseases mentioned here will not develop serious illness and will clear the infection themselves, knowing what to look out for will increase your chances to avoid complications althogether.

Lyme disease

Bacterial infection transmitted by ticks. If left untreated can cause serious neurological illness and plenty of other complications. First symptoms may include a round rash at the place of the bite that grows over time to resemble a bulls-eye pattern. Fever, flu-like illness, local paralysis may develop if the infection spreads to other parts of the body. There is no vaccine for this illness, but it is treatable by antibiotics. If you get a tick bite, remove the tick as soon as possible as it can take some time before the infection is transmitted. If you get symptoms some time after having been bitten by a tick, contact a health provider as early treatment is much easier than if the infection has been left untreated for a long time.

Tick borne encephalitis.

Viral infection transmitted by tick’s bites. Can in about a third of cases with symptoms cause neurological complications and even in rare cases death as it affects the brain and nervous system. First symptoms may include a flu-like illness some time after a tick bite that typically resolves but then disease returns with more debilitating symptoms. There are no effective medications for this disease but a vaccine is available.


A disease which is extremely rare thanks to vaccination. Tetanus is caused by bacteria found in soil that can enter the body through wounds and breaks in the skin. Although swimrunners may not be at higher risk than those doing gardening it is worth bring up since it is easily prevented. Disease symptoms include muscle spasms starting in the face and subsequently affects muscles in other parts of the body. If untreated the infection may be deadly. There is a good vaccine that is part of most the childhood vaccination program in most countries, but immunity may vain over time depending on the number of shots you have received. If it has been a long time (recommendations vary between countries) since your last vaccination you may need a booster shot.

Threats in the water

Bacterial infections

Infection by Escherichia Coli and Campylobacteriosis

Bacteria found in the gut of most animals and can contaminate streams and still or flooded waters. Outbreaks are often caused by ingesting water that have been contaminated by cattle feces. Symptoms for severe types of E-coli infection include low grade fewer and diarrhea, which may be bloody. Campylobacter symptoms are similar, but vomiting is also common. Small numbers of bacteria is needed to cause infection so infection can also be caused by transmission into your mouth from dirty hands.


Leptospirosis which can lead to Weil’s disease is a bacterial infection often spread to humans by contact with water contaminated with the urine from infected animals. Several outbreaks have been reported related to triathlon competitions (Denmark, Germany and Illinois). The bacteria can enter the body through the nose, mouth or eyes or by swallowing water, however getting the bacteria directly into the bloodstream via wounds and scratches is more likely to cause serious illness so make sure to cover any open wounds. Most people will only have mild disease or no symptoms at all, but if left untreated some may get very serious illness and it may even be deadly. Symptoms include high fever, vomiting, diarrhea, severe headaches, muscle pain and fatigue. Early antibiotic treatment will cure the illness.

Vibrio infections

Different species of vibrio bacteria can thrive in warm, brackish waters. Swimmers are at risk of serious infection if swimming with open wounds. Infection can cause infection of wounds and if the bacteria reaches the bloodstream it has a high fatality rate. Elderly or those with impaired immune systems are at higher risk of serious disease. Avoid swimming with open wounds. If you have wounds, cover them up with water tight bandages.

Swimmer’s ear

Swimmer’s ear is an infection of the external ear canal that can be caused by different types of bacteria found in water. Symptoms include pain, redness and itchiness in the affected ear which may also excrete discharge. Swimmer’s ear can be treated by antibiotic eardrops. Using earplugs may limit the risk by minimizing the amount of water that enters the ear.

Parasitic infections

Cryptosporidiosis and Giardia infection

Parasitic infections that are spread from animal (or human) feces through contaminated water. Symptoms of Cryptosporidiosis generally occurs within 10 days of exposure, while Giardiasis generally take longer often between one to three weeks. Both cause gastrointestinal upset and diarrhea which may be long lasting. Most people will clear a cryptosporidium infection by themselves while Giardia is often treated with antibiotics.

Swimmer’s itch

Itchiness of the skin and a rash after swimming may be caused by parasites called cercariae that normally infect many different animal hosts. The parasites are released from snails found in water and may burrow into the skin of swimmers accidentally on the hunt for their natural host. Cercariae parasites may be found in waters around the world. In northern climates they are more common in lakes and ponds during summer. The swimmer’s symptoms are caused by an allergic reaction to the parasites that soon after entry die in the skin. The condition rarely requires medical attention. You can control the itching with over-the-counter or prescription medications.

Viral infections


Norovirus, the same virus that causes winter vomiting disease can survive for some time in water. In times of floods, sewage systems may overflow and lead to contamination of rivers and lakes. Symptoms are stomach upset and vomiting. Normally the incubation period is only between one and two days. Symptoms may be quite debilitating, but most often resolve without treatment within three days.


In warm weather blue-green bacteria called cyanobacteria bloom. When this happens the water can be covered algae and the visibility will be decreased. For example the Baltic Sea experiences spells of this during summertime. Swimming in blooming algae can trigger itchy rashes, stomach upsets and, in severe cases, allergic reaction. If the water looks like it is blooming, avoid swimming in it.

Jelly fish

There are many species of Jelly fish that can cause more or less severe burns when touching uncovered parts of the body. In general the best advice is to avoid jellyfish as best you can, and if you get burnt, do not rub the area, rinse it with seawater (not fresh water as this may cause more poison to be released), but as different species may need different treatment always get to know the local species and what you need to do if stung, before jumping in. Goggles and wetsuit will offer good protection for the areas covered.

More info about diseases can be found at:

United States Centers for Disease Control and Prevention

European Centre for Disease Prevention and Control

Anders Wallensten /