top of page




Nutrition can affect sport performance in a variety of ways.  There are over 50 nutrients the body requires on a daily basis.  There is no perfect diet, but the optimal is one that keeps the athlete well hydrated, provides adequate calories, and supplies the 50-plus nutrients in the needed amounts.  No single food or supplement can meet these requirements.  They are best achieved by consuming a wide variety of foods on a daily basis.  A proper diet is essential for maintaining energy levels, developing muscles, and increasing endurance and strength.


The most important nutrient for the athlete is water.  Water is necessary for the body’s cooling system.  It transports the body’s nutrients throughout the tissues and maintains adequate blood volume.  During intense or prolonged exercise, the body’s thirst mechanism lags behind actual need, thus it is important to make a conscious effort to drink water long before thirst occurs.  When swimming, it is difficult for a marathon swimmer to gauge how much fluid loss is occurring.  Therefore, it is extremely important to drink fluids regularly during a marathon swim. During events lasting longer than 3 hours, electrolyte replacement is also necessary.  “Sport Drinks” are ideal to replace fluid sodium, potassium and carbohydrate losses.  Salt tablets should be avoided.  Quick energy foods, such as chocolate bars, should be avoided as they may cause retention of fluids in the digestive tract possibly causing nausea, cramps, and dehydration.


Most long-distance swimmers have heard of “hitting the wall” or have actually experienced the sensation.  This sudden, overwhelming wave of physical and mental fatigue strikes when the body’s energy reserves in the form of carbohydrates are all but exhausted.  Intense or prolonged exercise can markedly deplete the body’s energy reserves within a few hours, depending upon the athlete’s fitness level and on the amount of reserves in the body.  When this happens, the muscles cease to function efficiently, the athlete experiences extreme exhaustion, and confusion or disorientation can occur.


Marathon swimmers can avoid or minimize the effect of “hitting the wall” by consuming carbohydrates during the swim in the form of easily digestible liquids.


NOTE:    Do not experiment with new foods just prior to or during the swim as they can adversely affect the digestive system and lead to cramps or vomiting.  The appropriate time to test the suitability of foods is on the Trial Swim.


The most important rule to remember is to keep well hydrated, both before and during the marathon swim.



Hypothermia is a condition caused by the lowering of the internal body temperature. Specifically, a hypothermic person is one whose core temperature registers below 34.5°C (94°F).


On a long-distance swim, the potentially most dangerous problem comes from the swimmer suffering hypothermia. It can be lethal, and it requires immediate and specialized medical care.


As the swimmer’s body temperature declines, certain symptoms occur such as shivering, slurred speech, slow breathing, clumsiness, confusion, disorientation, amnesia, sleepiness, and irritability. In addition, hypothermia can cause impairment of sensory functions and motor performance, reflected in marathon swimmers by an unusual stroke pattern and/or "directional instability" (trouble swimming in a straight line).


One of the dangers to those who are monitoring the progress of the swimmer is distinguishing between hypothermia and extreme fatigue, both of which commonly occur with marathon swimmers. With proper safety precautions, a swimmer with a normal core temperature can swim to a point of near exhaustion without jeopardizing their health; however, if the swimmer is suffering from hypothermia, and not from extreme fatigue, and is allowed to continue, then tragedy can result.


Death from hypothermia is cardiac in origin, and this is the most important physiological disturbance to occur in cold water.


The rate of heat loss from the body is caused by two factors. The first is the rate of heat transfer from the body core to the skin. This rate is influenced by the degree of blood flow and the amount of tissue insulation. Abundant amounts of subcutaneous fat will improve the body's ability to conserve heat.


The most important factors influencing the development of hypothermia in marathon swimmers are:

(1)   Amount of subcutaneous fat and body surface area.

(2)   Water temperature.

(3)   Duration of swim.

(4)   Amount of body and water movement.

(5)   Body heat production, which depends to some extent on the number of calories and fluid ingested.


Resistance to cold in marathon swimmers depends primarily upon the thermal insulation provided by their subcutaneous fat. Other important factors are body size and body heat production. These three factors together are mainly responsible for the maintenance of thermal balance in cold water.


Solo Swims includes a low-temperature thermometer in its First-Aid Kit. 

SSO also offers the CorTemp monitoring system. It allows the Swim Master to measure the swimmer's core temperature while the swimmer is in the water, without touching the swimmer.

  • The CorTemp® Ingestible Core Body Temperature Sensor (pill) is swallowed and it wirelessly transmits core body temperature as it travels through the digestive tract. The sensor’s signal passes harmlessly through the body to the CorTemp Data Recorder.

  • The silicone coated sensor (pill) contains a micro battery, quartz crystal, communication coil and circuit board, all encapsulated in medical grade epoxy.

  • The sensor passes through the body at the subject’s normal rate of motility which can vary anywhere from 24-36 hours.

  • The CorTemp sensor is accurate to ± 0.1°C and is FDA cleared and registered as a single use device.


The following are the signs and symptoms of hypothermia by temperature range.


Signs and Symptoms of Hypothermia



  Core Temperature            

  °C                °F

37.0              98.6                 Normal body temperature

36.9 - 36.1    98.4 – 97.0      "Mild" Hypothermia: Goose bumps, Sporadic shivering.

35.5              96.0                 Uncontrollable shivering

35.0              95.0                 Voluntary tolerance limit in non-fatigued swimmer. Deep cold. Numbness. Blue skin         


34.9 - 34.3    94.9 – 94.0      "Moderate" Hypothermia: Mental confusion begins. Motor performance impaired: slurred speech,                                                                incoordination, “claw hand” or other muscle stiffness. Skin may be grey.


32.8               91.0                Severe mental confusion. Grossly impaired motor performance. Shivering impaired.


32.2 - 31.1     90.0 – 88.0     "Severe" Hypothermia :Heart rhythm irregularities. Severe disorientation, hallucinations. Rapid                                                                        deterioration in motor performance: drop in stroke rate, hip drop, or directional instability. Dilated                                                                   pupils. Grey-white skin. Shivering stops


31.0 - 30.0     88.0 – 86.0      Loss of consciousness. No response to pain.


28.0               82.4                 Ventricular arrhythmias


<26.6            <80.0                Death

Early Season Advice


Unless the swimmer has a coach experienced in marathon swimming, the swimmer will have many questions.  The swimmer usually has an amateur competitive coach who is willing to offer some extra time and come on the swim.  For the purposes of motivation and safety, it is essential for the Coach to have had a close working relationship with the swimmer. In the event of the gradual onset of hypothermia, the effectiveness of questions to test alertness depends on the swimmer's background (age, technical knowledge, arts knowledge, medical conditions such as Asperger’s Syndrome, etc.).


The following information is specific for marathon swims across Lake Ontario from south to north.



Physically, the swimmer should swim with a competitive swim club for at least 6 workouts a week until about March.  Weight training, particularly exercises designed to strengthen the core and the rotator-cuff muscles, is an important addition to the training programme. In March or April, the emphasis switches from speed to distance, building up to 45-50 km per week by the end of May.  In June, the venue switches to small warmer lakes with a “long swim” of 12-16 km every weekend and 6-8 km on weekdays for a total of 50-60 km per week.  These long slow distance (LSD) workouts can be varied by timed swims of varying distance, with kick sets, or with “fartlek” intervals.  Fartlek means slow/fast and refers to a continuous swim with sprint sections alternating with brief slow “rest” sections.  One or two interval workouts in the pool per week help maintain speed.  The strokes can be varied but most swimmers find front crawl to be most efficient and least wearing on the joints for LSD swimming.  Breaststroke doesn’t maintain body temperature or speed against a headwind.  Helping a back-stroker swim in a straight line in open water is difficult for the crew.  Treading water holding a brick, working up to 10 minutes daily, is good preparation for feeding times.  In mid to late June, Lake Ontario warms up to over 14°C and as many workouts as possible should be in the lake.  It is helpful to the swimmer’s confidence to have completed at least one 16 km (10 mile) swim before the Trial Swim.  Three or four weeks before the big swim, a 26-30 km (16-20 mile) swim does wonders for the swimmer’s confidence (and conditioning). Care should be taken not to damage the joints (stop if there is undue pain) and to rest the day before and one or two days after.  Finally, for those who really want to simulate the muscular fatigue of a 52-km swim, a 16-km swim in a short sleeve sweatshirt, sweat pants and sneakers can be tried.


Open Water:

Open water swimming presents challenges to which the swimmer should become accustomed before the big swim.  The only way to get used to waves is to swim in all kinds of weather (except thunderstorms and fog).  One pre-swim application of sunscreen cannot protect a swimmer from sunrise to sunset. Therefore, a tan should be slowly built up. Learning to swim in a straight line and only looking-up about every 10th stroke is a challenge for some.  Bilateral breathing is an asset (prevents unilateral sore neck and enables the swimmier to breathe downwind in huge waves).  The swimmer should get practice swimming beside a boat at 2-3 metres away.  With practice, they can judge the boat’s angle and distance while breathing to the side and adjust their stroke without stopping. Night swimming should be practiced at least once in a familiar lake with a familiar boat and driver.  For those who find it frightening, they should keep practicing night swimming until the fear dies down.  At night, the swimmer should have attached a chemical glow stick (Cyalume®) or be illuminated from the boat.  Also, at night the swimmer should swim closer to the boat, at about 2 metres.



Open Water Safety:

Open water swimming also presents dangers.  The swimmer should never swim alone because of medical risks (cramps, heart problems, seizures) and the possibility of being run over by a boat. Swimming parallel to shore is acceptable, if supervised by someone walking on shore.  When swimming in open water, water-safety equipment (throw rope, floatation device, life jackets, and/or swim ladder) and re-warming equipment (blankets and hot drinks) should be available.  Boat drivers should always take care to switch the boat into neutral when talking to the swimmer.  Wind and waves necessitate keeping the boat further away from the swimmer.  The workout may need to be called off if the boat has difficulty negotiating the waves and the spotter cannot see the swimmer at all times.  A swimmer should also learn to stay closer to the guide boat when surrounded by heavy boat traffic.



Open water swims are a good opportunity to train pacers.  Furthermore, pacers also need to acclimatize to waves and cold.  Most front crawl swimmers prefer their pacer to swim about one head ahead of them and about an arm’s length away.  When the pacer is a little ahead, it is motivating to the swimmer.  The pacer should never be behind, as the swimmer slows down when he or she looks backwards.  Most swimmers also find it motivating if the pacer matches the rhythm of their arm pull to the swimmer’s rhythm (on the swimmer’s breathing side).  Thus, it appears that an invisible string from the pacer’s arm is pulling the swimmer’s arm through the recovery phase.  The pacer may need to drag their feet and/or adjust the length of their other arm’s stroke to be able to keep up this rhythm.  The best pacers match the swimmer’s rhythm initially but then subtly pick it up and keep it speeded up.  Smiling during breaths or underwater can pick up the swimmer’s morale.



Cold water is part of what makes Lake Ontario one of the five toughest swims in the world.   (Being blown past Toronto is the other reason).  Lake Ontario is very deep, up to 200 metres in places.  Most of this vast body of water is at 4°C year-round.  Only the surface layers warm up with warm weather.  The different layers are called thermoclines.  The depth of the top warm layer varies tremendously from year to year.  A strong wind can churn up the lake and bring the cold water to the surface in a matter of hours.   The temperature can go from 20°C to 10°C from one day to the next.  This can even happen during a swim, pockets of cold water may be left over from the last storm, a freighter may have churned up cold water for a ½ km swath, or the 5-8 kilometres near one shoreline may be cold due to wind effect.  Therefore, the swimmer has to be acclimatized to swimming in cold water.  Cold showers and sleeping with open windows all winter are not necessary as the body only needs 1-2 weeks to acclimatize.  Swimming in Lake Ontario from 14°C and up daily for 4-6 weeks usually suffices.  Care should be taken to avoid hypothermia by limiting the duration of very cold workouts or by coming out when the swimmer can’t stand it any longer.  This “voluntary tolerance limit” can be increased by longer exposures every swim.  A cap and ear plugs reduce heat loss and prevent hypothermia.  Don’t forget that swimming faster keeps one warmer. The ability to resist hypothermia is a measure of fitness and body fat.  Swimmers must rewarm immediately when muscles start to cramp. “After drop” is the phenomenon where the body’s core temperature drops during re-warming because cold blood from the extremities is returning to the core.  Because of this effect, some means of re-warming should be available at all cold-water workouts (blanket, hot drink in thermos, car with heater).  Don’t forget to take off wet clothes.  Care should also be taken to enter very cold water slowly to prevent heart arrhythmias or choking.  Walk in, splash the face and neck, and then bob up and down before swimming.

Penny Lee Dean, in her book Open Water Swimming, recommends that the coach should have a discussion with the swimmer, at least 2 months before the swim.  The coach asks about 25 to 40 personal questions from the past such as names, dates, colours of bikes or cars, favourite subjects, mother’s birthday, etc.  The coach writes these down and brings them on the swim to test the swimmer’s orientation and ability to think, if hypothermia is a question, as this is a very important symptom to monitor.


Weight Gain:

Should swimmers gain weight for more insulation?  If they are very lean, (less than 12% body fat for males; 16% for females), they could do this gradually throughout the season.  If they have the average amount of body fat, they could wait until about 2 weeks before the swim to decide.  The anticipated water and air temperature will be the deciding factors.  It is a strain on the heart to carry the extra weight throughout the training season.  In the end, cardio-vascular fitness is probably a greater factor for success than above average body fat composition.


Psychological Factors:

Psychological preparation is the key to pushing the body beyond all limits.  The swimmer should start by setting smaller goals, for example, the Trial Swim, the 26-30 km swim (“I can do more than half the Lake”), and the sweatshirt swim (“I can take the fatigue”).  They also need to imagine the big swim during workouts -  for example, imagining how they will cope with the last 8 km and how the finish will look and feel.  Visiting all potential finishing sites is enormously helpful.  A large nautical chart of Lake Ontario on the wall helps them “Think Lake Ontario” at home. How does a swimmer cope with the long hours of mental monotony?  Everyone develops their own solution during LSD training.  Some count, some memorize songs or poems ahead of time, some engage in elaborate fantasies and others have the ability to “space-out” in a kind of self-hypnotic state.  Pre-swim anxiety can be managed by practicing relaxation techniques ahead of time.  Everyone has their “ideal performance state” for peak performance and too much anxiety can be detrimental (loss of focus, insomnia, migraines).  The swimmer should share their dreams, goals and motivational statements with the coach, preferably in writing, for use during the swim.


If the swimmer is under 18 years of age, it is strongly recommended that the Swim Master meet with the parents and explain the risks and safety precautions as well as answer all their questions.


Swimming Equipment:

The swimmer can be testing out their swimming gear during workouts.  Tinted, ultra-violet filtering goggles for daytime and clear goggles for night-time should fit well and stay on in waves but not cause eye or head-ache on long swims.  They can be pre-treated with anti-fog liquid.  Neoprene is not allowed for the swim cap but more than one can be used (recommended in cold water).  Silicone-rubber caps are thick.  Choose bright colours for visibility. “The swimsuit cannot aid in buoyancy or warmth”.  Wetsuits are not allowed.  The swimsuit should be comfortable and not cause excessive drag (should fit high up the chest and snugly in the small of the back for women) nor rub (avoid wide shoulder straps for women and tight leg openings for men).  Being clean-shaven reduces shoulder rub for men. Lanolin or Vaseline applied to the neck and armpits for women and to the neck and groin for men prevents nasty rub marks during training.  Custom earplugs are expensive and may require lanolin or Vaseline to provide a seal.  Wax or silicone earplugs can be moulded and are cheap enough that extras can be taken.  Earplugs and swim caps reduce heat loss tremendously.  On the big swim, extras of all of the above can go in a bag with a towel in the Zodiac to accompany the swimmer.



Swim Food:

Exercise physiologists have concluded that for events lasting greater than 3 hours, where the exercise intensity is 30-70% of maximum, the nutrition concerns are:

1.  Glycogen replacement;

2.  The prevention of dehydration; and

3.  Hyponatremia (dangerously low sodium in the blood which occurs when only water is consumed). 


     To this list, the marathon swimmer must add therevention of hypothermia.


The American College of Sports Medicine recommends that the average 70 kg endurance athlete drink 500-1000 ml (2-4 cups) per hour of electrolyte replacement drink containing 6-8% carbohydrates (60-80 g per litre), 20-30 mEq per litre of Sodium, and 20-30 mEq per litre of Chloride.  Since the marathon swimmer probably sweats less than the marathon runner, the swimmer’s fluid requirements may be at the lower end of the range, i.e. 2-3 cups (500-750 mL) per hour.  Hypothermia causes the body to burn extra calories; therefore, the carbohydrate requirements may be at the upper end of the range, i.e. 80 g per litre.  Also, in cold water, a swimmer’s drinks need to be warmed.


The swimmer has a choice in planning “swimming food”.  They could either drink the perfect carbohydrate-electrolyte replacement drink (Gatorade reconstituted from powder, in 750 mL, instead of 1000 mL) for the whole swim or they could mix and match clear fluids with higher calorie drinks on each feeding, as long as the fluid replacement totals 2-4 cups per hour and there is some salt (electrolyte) content.  The problem with Gatorade-like drinks alone is that this may not provide enough calories, especially if the swimmer weighs more than 70 kg.  Also, Gatorade is not tasty when warm.  The problem with solutions more concentrated than 8% carbohydrate is that they delay stomach emptying (normally taking 20-30 minutes for water) causing a sensation of fullness or even nausea.  This may be more of a concern towards the end of a swim.


SSO recommends a variety of cold and hot milk-based, fruit juice-based, and sweetened clear fluids as well as carbohydrate-electrolyte replacement drinks.  Examples include Ensure, Boost, fruit sport drinks, blended canned peaches with corn syrup, blended canned fruit cocktail, blended soup, cup-a-soup without noodles, tea, coffee, juice, soft drinks and Gatorade.  New high energy products are PowerGel and GlycoMax.  Some swimmers like Boost (comes in blueberry) and Ensure, but many of the ingredients in these drinks are unnecessary and the heavy milk content can be hard to digest.  Too much pure fruit juice should be avoided as fructose (fruit sugar) can cause gastrointestinal distress.  Carbonated beverages are OK only after they go flat.  The important thing is to try out different “swim foods” on the longer training swims.


     Solids should be avoided for many reasons.  Waiting to finish chewing makes the feeding break too long and the swimmer cools off.  Solids delay the emptying time of the stomach leading to nausea.  A few hours into the swim, the intestines will also be having trouble digesting complex foods, leading to nausea.


Swim Organization:

The other important things a swimmer should be thinking about in the Spring are selecting a coach, a manager, 2-4 pacers, a First Aider, and recruiting large boats.   Finding suitable large boats is difficult and the swimmer should start early.


Should relatives/lovers come on the big swim?  There comes a point in almost every swim where the swimmer begs to come out.  If the swimmer and relative both swear that they will respect the coach’s and Swim Master’s opinion that the swimmer can still be pushed, then it might be workable.  It helps if the relative has a job to do on board a big boat.


Many swimmers add personal meaning to their swim by raising money for a charity.  Larger charities can help more with organization and costs, but also expect more from the swimmer.  It is important for the swimmer to advise the charity that the swimmer’s success depends on good weather and that the date and time are subject to change.


Advice For The Last Month

Once the 24-30 km swim has been accomplished, the training focus shifts to maintaining conditioning and cold acclimatization, avoiding injuries, and to psychological preparation.  Suggested joint injuring activities to avoid include: swims longer than 15 km; choppy waves and weedy swimming; contact sports; and water skiing.  Getting enough rest and staying healthy is important.  Organizing the swim and the pre-swim meeting in the last month help with picturing how things will work on the swim, but they also increase anxiety.  Having a trustworthy manager to assist reduces the load.  Relaxation exercises and positive self-talk (available from Dr. Korzekwa) may also help.


The last 1-2 weeks is the time to gain weight, if necessary.  Carbohydrate loading is not recommended.  A 52 km swim in polluted water is very hard on the digestive system and any upset in the balance that has been achieved during training is to be avoided.  Furthermore, carbohydrate loading only provides an advantage for 3-5 hours.  Also, the strategy has been proven ineffective for female athletes.  (If males want to try it, the carbohydrate-depletion portion of the diet should be dropped, as it is dangerous and not necessary.  Only the carbohydrate loading component needs to be done for 3 days prior to the event.)  The diet on the day of the swim should be very easy to digest: no fibre, low fat, and neither gas forming nor spicy.  The last meal should be no closer than 3-4 hours before the swim.  Sugar should be avoided in the last 2-3 hours as it causes insulin secretion, which causes glycogen breakdown and premature fatigue.


When preparing for the swim, the swimmer should be cautioned that they will be disqualified if caught ingesting banned substances (See The Swim Master reserves the right to inspect all medications offered to the swimmer in order to enforce this rule.  Use of medications not listed on the Medical Form and not pre-approved by the SSO Medical Officer may result in withdrawal of SSO sanction, or in termination of the swim.

What starting time should the swimmer plan for?  This is a controversial topic.  The answer depends to a large extent on the speed of the swimmer and the weather. Sometimes the weather for the weekend only allows one 21-24 hour “window,” so there is no choice.  If the forecast is for wind, the swim will take longer.  The average swimmer who completes the 16 km Trial Swim in around 5 hours will take about 18-22 hours to swim Lake Ontario.  Once the test swim gets close to 6 hours, the Lake time will be 24 hours or more, which means a night period is guaranteed.


The pros and cons of starting at sunset (9 pm) are:

Pros:     Set up and start is in daylight (reducing confusion); the coldest part of the swim (due to air temperature) is over first; the most dangerous part (night) happens when the crew and swimmer are fresh; the ending (for the average swimmer) is in daylight; and, if the crew assembles right after work on Friday, they have the best chance of catching the weather window for the weekend;

Cons:   9 pm is the end of the day and people are starting to tire; the swimmer has to have been able to nap; if the swim starts late or takes longer than 24 hours, it runs into darkness again.


The pros and cons of starting at sunrise (6 to 7 am) are:

Pros:     The swim can take up to 38 to 39 hours with only one night period; the ending may be calmer at night (allowing for progress against wind);

Cons:   No one gets a good night’s sleep unless they can spend the night on Niagara-on-the-Lake; set up is in the dark; the coldest and most dangerous part of the swim is in the last 6-9 hours (21-24 hour swim) when the swimmer and crew are exhausted; and the finish is in the dark (causing confusion).


Most swimmers opt for a start at sunset and the swimmer spends the day in Niagara-on-the-Lake trying to nap.


Once the large boats have been confirmed, final equipment and crew organization can begin.  If possible, the pre-swim meeting should be held. If the meeting cannot be held, the swimmer or manager needs to ascertain that the necessary equipment and items (see Crew & Equipment) are on board.  They also should enquire about the facilities on board to plan the menu, walkie-talkies, cellular phones, lighting system, number of crew, amount of gas, and room for extras (e.g. paddle board).  The Swim Master should try to get Captain’s Information Packages (available from SSO) to the boat captains.


Another important equipment consideration in the last month is the grease.  Swimmers generally use anhydrous lanolin however, there have been concerns about toxins in lanolin (Wool fat) that have led to its reduced availability.  The swimmer should insist on anhydrous lanoline, since hydrous lanoline is runny and does not stay on.  Anhydrous lanolin sometimes cakes off but most of it remains, especially under the suit.  Vaseline by itself tends to rub- or melt-off.    Anhydrous lanolin may be blended with a little Vaseline, which also works well.  The anhydrous lanolin usually needs to be ordered in advance through a pharmacist. Five to eight 500 g jars should suffice. For the big swim, packing the jars in a bag with 2 pairs of rubber gloves, a roll of paper towels and an old sheet for the swimmer to sit on in the car is helpful for clean-up.  Swimmers may want to practice swimming with grease to get the feel of it and test for allergies.  Especially important to remember is the fact that grease from the hands can smear goggles and ruin the seal of goggles and cap.


In the last few weeks, the swimmer or manager has to contact the Toronto Port Authority and the marinas.  Rental or transport of inflatables also needs to be arranged.  Finally, the Boat and Crew Confirmation Forms (see Forms) should be submitted to the Swim Master at least 2 weeks before the swim.

bottom of page