Medical Notes

The following medical notes about the potential risks for swimmers competing in the Rottnest Channel Swim have been provided courtesy of Dr David E Davies MBBS., FANZCA., Dip.DHM.

Heat Illness

During exercise it is important that the body’s core temperature is kept within a narrow range. When an individual’s core temperature moves outside of this range, the body’s capacity to perform strenuous physical activity is reduced.

When exercising in hot conditions the body attempts to regulate body temperature mainly by sweating and evaporation. Swimmers need to be aware that if the conditions on the day of the swim are humid, these heat regulation mechanisms are not as effective.

Swimmers who are in teams can prevent heat illness by wearing light weight, well ventilated clothing while not swimming, spraying water on their skin and exposing the body to air flowing across the body. Individual swimmers can keep cool by taking regular drink breaks and scheduled rest breaks. All swimmers should try and stretch where they can to help relieve muscle cramps.

Heat illness has 3 separate degrees of severity:

Dehydration – symptons include loss of energy, muscle cramps, thirst, diminished performance and headache.

Heat exhaustion – symptons include headache, nausea, feeling faint of dizzy, cramping, chills and clammy skin.

Heat stroke – is characterised by high body temperature, confusion or loss of consciousness.

To treat dehydration and heat exhaustion drink fluids, lie the swimmer down and rest the swimmer under shade. If their condition deteriorates, seek medical help immediately.

If a swimmer is showing signs of heat stroke, remove them from the water, seek immediate medical assistance, lie the swimmer down under shade and cool them by applying wrapped ice packs to the armpits and/or groin.


Humans can cool 4-5 times faster in water compared with air at the same temperature. Although the water temperature in the Perth area in February is 20-22 degrees Celsius, a number of swimmers still get cold during long ocean swims.

Blood vessels in the skin contract in response to the cold, however, blood vessels of the scalp do not, causing a larger proportion of heat to be lost by this route. It is advisable that swimmers wear and impervious bathing cap under the official race cap, to minimise this heat loss.

During a long swim the body temperature is maintained largely by metabolism in the muscles. If the muscles do not receive enough energy they will be less able to work and will generate less heat. It is essential that swimmers make regular, short stops to replace this energy by eating and drinking warm high-energy foods and fluids. The digestion of these generates heat and supplies the energy that the muscles require for maximum efficiency.

Nutrition stops should be kept brief as skin blood flow increases during exercise resulting in increased heat loss. During exertion this loss is balanced by the increased muscle activity but when the swimmer stops the heat loss is much greater than the heat gain from reduced muscle work.

It is the duty of the support crew to watch out for signs of hypothermia in their swimmer at all times. In the early stages of hypothermia, even before the swimmer feels cold, the swimming action may become uncoordinated and the swimmer may be unable to maintain a straight course. During food stops the swimmer may be shivering uncontrollably, appear vague, unable to concentrate or to understand instructions, act irritably and irrationally. As the hypothermia progresses, the swimmer may be unable to raise his/her head or arms out of the water, unable to obey commands or answer questions appropriately. Under these circumstances the swimmer should be removed from the water immediately.

Children and seniors are more susceptible to hypothermia and should be watched closely. The victim of hypothermia should be handled gently, as rough handling can result in heart rhythm disturbances. Remove the swimmer from the water as gently as possible. He/she should them be dried, wrapped in towels and blankets and protected from the wind. A large plastic garbage bag of sheet should form the initial layer next to the skin and the blankets placed over this. This not only avoids getting wool fat on the blankets but also insulates much more efficiently. Shared body heat may also be appropriate.

If the swimmer is conscious they should be encouraged to eat and drink small quantities or warmed fluids frequently. DO NOT GIVE ALCOHOL as alcohol increases the rate of heat loss by dilating the blood vessels in the skin. If the swimmer is unconscious then place in the coma position, maintain the airway, and do not give fluids or food. Seek urgent medical attention form a doctor on the course.

Any swimmer who is thought to be suffering from hypothermia must be seen by a doctor as soon as possible.

Marine Stings

Stings from marine jellyfish are a way of life in open water swimming. Problems arise if the sting is to a sensitive area such as the cornea of the eye or if the tentacle becomes trapped inside the bathing costume. It is strongly recommended that swimmers wear goggles at all times while in the water.

Fortunately no marine jellyfish in the Perth region is lethal. The most common nasty jellyfish around Perth is Carybdea rastoni, locally know as a ‘stinger’. Its tentacles are approximately 10cm long but the body is only 1-2cm across. It is almost transparent and very difficult to see in the water. In summer, stingers can be in large numbers along the beaches. This jellyfish tends to swim closer to the surface at dawn or dusk and during cloudy periods. In bright sunshine it swims deeper.

The sting causes an immediate severe burning sensation of variable intensity that may last for several hours but usually recedes over about 30 minutes while the swimmer is in the water. But it may return when the swimmer leaves the water. This is associated with a skin wheal that may persist for one to two weeks with minor skin discolouration persisting for several months. Some individuals may also have an allergic response to the sting.

Management of the sting is to initially douse the area of the sting liberally with vinegar then apply ice directly to the wheal to ease the pain (vinegar destroys still-active stinging cells). A cold shower has the same effect as applying ice. Do not rub the area with sand as this causes more toxin to be absorbed. Temporary relief may be obtained from ‘Stingose’, or a roll-on underarm deodorant applied to the wheal. A local anaesthetic cream or spray may help if the pain persists and, for severe wheals with skin damage, a steroid cream such as Betamethasone or hydrocortisone may be indicated.


Seasickness is a common complaint among open water swimmers, especially in rough conditions. This is probably due to the motion on the water surface combined with the swallowing of salt water and fuel residue.

Management of seasickness is initially reassurance and possibly altering the breathing pattern to reduce the intake of salt water. If vomiting persists there is a real possibility of dehydration and cramp. A swimmer who is persistently vomiting will probably need to be withdrawn from the water.

A swimmer can reduce the susceptibility to motion sickness by undertaking long training swims in the ocean prior to race day. This is not always effective as sea conditions are infinitely variable, however it does help. Medication may help but if you do use something, make sure you try it out before race day as most of the motion sickness medications have side effects. These side effects can range from dry mouth through amnesia, hallucinations, blurred vision, to severe migraine headache depending on the drug and dosage. Consult your medical practitioner well ahead of time for advice.

Support crew who suffer seasickness should try sitting on the deck close to the waterline and watching the horizon. Being overdressed, too warm, in a stuffy environment, eating too much, and drinking alcoholic drinks will aggravate seasickness. A seasick person should be lightly dressed, slightly cold, have plenty of fresh air, eat small amounts of dry digestible food before and during the crossing and avoid alcohol.

Please note that it is not the responsibility of official boats to transport seasick passengers to shore.


Perth has a reputation for being one of the sunniest cities in the world and there is little atmospheric protection from the sun’s rays. The average temperature during the day in February is 30degrees Celsius and the ultraviolet factor is extremely high.

The sun will burn in the same way as fire, except we are not aware of the burning sensation. People with fair complexions are most susceptible to sunburn and should take extra precautions.

Sunburn can occur even after a relatively short exposure, especially during the middle of the day. Frequent application of a water resistant, sun protection cream (UV factor 16 or higher), a wide brimmed hat and cool, loose fitting cotton, long sleeved shirt is recommended.

Solo swimmers should apply sunscreen at least 15 minutes before the wool fat so that it is not washed off. Zinc cream seems to wash off less rapidly than most other creams. Take care to apply sunscreen to all exposed parts such as the face and nose, behind the ears and the neck, backs of the knees and thighs and the soles of the feet.

Reflected sunlight from the water can create problems and support crews should apply sunscreen to exposed areas, even though they are wearing a hat. Remember, a peaked cap does not provide protection to the sides of the face, the ears or the back of the neck.

The consequences of severe sunburn are dehydration, severe pain and a possible stay in hospital. Most cases of sunburn can be dealt with by taking a cool bath or shower, and applying cool compresses (although not iced as this may chill) to the most affected parts. Calamine lotion or one of the commercial anti-sunburn moisturising creams will usually help. Paracetamol may reduce the pain, but if the sunburn is severe, cold shivers and a temperature may develop. If the sufferer is a child, medical advice may be necessary.

Sharp trauma

There is a risk that the propeller of the escort craft can cause injury, especially in rough conditions and when the boat is manoeuvering close to the swimmer or during team changes. It is the responsibility of the boat skipper to keep clear at all times.

Should any form of cutting injury occur, remove the swimmer from the water immediately, elevate the effected area, cover with a clean towel and apply direct pressure to the wound to stop the bleeding. Seek medical attention urgently from the doctor on course.

Blunt trauma

Blunt trauma to a swimmer is only likely if, in rough conditions, the escort boat gets too close to the swimmer and is dumped onto the swimmer by a wave. Management will depend on the severity of the collision and the condition of the swimmer. If there is any head injury, however minor, the swimmer should be withdrawn from the water and be seen by a doctor on the course.


Exhaustion is characterised by a floundering action where a swimmer is unable to raise his/her arms or is not responding to questions or directions. Taking the swimmer from the water will usually see him/her recover from this problem. A doctor should examine the swimmer as a precaution against a more serious injury.

Administration of medications by non-medical persons

All medications, including prescription and those available over-the-counter, can have serious side-effects. These side-effects may become a problem when the body is placed under additional stress caused by physical activity.

For more information about the administration of medications by non-medical persons go to the Sports Medicine Australia web site.