Every morning before the sun rises, Canada's upper echelon of swimmers plunge into the lukewarm Toronto Pan Am Centre pool. After a recovery and feeding period, 19-year-old Stephanie Horner and her counterparts are back at it again and in the pool for the afternoon. For long-distance swimmers like Horner, her freestyle strokes during a training session last until she reaches a distance of eight kilometres, and sometimes more. By week's end, a marathon swimmer could log as many as 100 kilometres. Horner is a greenhorn when it comes to swimming marathons. The former pool swimmer has accumulated less than 10 long-distance races; her teammate Richard Weinberger has competed in more than 50. Both will compete in the 10-kilometre swim in the unreliable and lapping waters of Rio for the marathon swimming event taking place next Monday (women's) and Tuesday (men's).

Through all the training, the early mornings, the feedings, the grueling kilometres Horner and her comrades rack up, almost nothing can prepare them for mowing through arduous loads and working long periods in isolation in the pool. It's just them and a chlorinated haze of water. Isolation has the potential to produce athletes that become bored, often finding it difficult in executing the repetition required to progress to the next level. It can also force a swimmer to give up during competition or quit altogether.

Steve Price, one of six coaches on the Canadian Olympic swim team, tells me his marathon swimmers work with mental skills coach Whitney Sedgewick, who helps them deal with things like how they will overcome bouts of solitude when training in the pool or in competition in open water. Sedgewick arms the swimmers sometimes with contingency plans to block out fears and other mental demons that occur during lengthy spells in the water; especially when energy levels have been depleted.

"It is long hours. It's not scripted. Your body shuts down," Price said.

Swimmers like Horner and Weinberger will often spend a large chunk of their morning and afternoon sessions alone, plunging arms into their lane, slapping the water, and striving not to slip into a mental state where feelings of seclusion can rot their discipline. Price said in order to combat the remoteness, he'd send other swimmers into the lanes next to them to keep the duo company in an effort to break the feeling of being detached.

"But concentration levels wear out. Then mental exhaustion, it happens," he said. "It's the nature of the 10-kilometre swim."

The Olympic sport of marathon swimming is 10 kilometres long, unlike the marathon run which is set at 42 kilometres. Athletes can also embark on solo swims, where they try to break a world record or feat, or they race in competitions for world rankings. Like marathon running, the sport of marathon swimming is laborious. Swim routes take place in open water settings: oceans, lakes, channels, canals and straits. It's a sport unlike any other, where you become the enemy and the struggle is against yourself. In the water, you are completely removed from the real world. Every third or fourth stroke you hear the rumble of a boat engine and get a whiff of diesel, but then your head sinks back under the water and everything becomes white noise and muffled.

Canada has provided a long history of marathon swimmers. George Young from Toronto was the first to win the 32 kilometre Catalina swim in 1927 and was the main reason why the marathon swim was inducted at the Canadian National Exhibition that same year. During the 1950s, Marilyn Bell became iconic after she was the first woman to complete 42 kilometres between Atlantic City and New Jersey, and also swam the 64 kilometres required to cross the choppy and tousled Lake Ontario. Cindy Nicholas dominated the 1970s with a record crossing of Lake Ontario at 16 years old and then crossed the English Channel the following year—her first of 19 crossings of the shallow sea.

In 1988, the world came to know Winnipeg native Vicki Keith. It was the year she completed a double-crossing of Lake Ontario in 56 hours and 10 minutes with a glow stick tied to her back so crews wouldn't lose sight of her. It was her first attempt at that feat and was her first large swim at night. It was one of the first encounters where she had to confront relentless feelings of being severely isolated.

"I remember at one point realizing I was swimming in freshwater but my goggles were filling up with salt water because I was crying, I was in tears, I was alone. I was by myself even though I had boats around me. But the battle is yours and yours alone," said the 55-year-old. "Every sense that you have is dampened. There's so many things playing into it, not just being alone—but being alone and miserable, or alone and cold, exhausted or sore. And you put them all together and that's when it becomes really intense."

Keith's isolating experience didn't hold her back. The Terry Fox Hall of Famer—an achievement that recognizes outstanding Canadians who have made extraordinary contributions to enriching the quality of life for people with physical disabilities—went on to claim 18 world records, was the face of Canada's marathon swimming, became the first person to swim across all five Great Lakes, and is the only person to complete the 104 kilometere double-crossing of Lake Ontario. Keith now teaches athletes with disabilities how to swim marathons and wrote a book on the psychological effects of marathon swimming that helps offer skills on how to swim alone.

"Singing was the one thing I found that was useful when I was emotionally and totally devastated. Just words that could block the voice inside my head that was telling me I was exhausted and I couldn't go on," she said, acknowledging that sometimes the pain can be mental but can become apparent in a physical manifestation. "You have to find strength even when you're at your emotional lowest. You have to find strength somewhere or you're done."

British swimmer Ben Hooper will be attempting to be the first person to swim across the Atlantic Ocean from Africa to Brazil later this year. Although not a competitive swimmer, the former police officer has clocked up some serious mileage, swimming 2.8 million meters in 2014 (which roughly equates to 115,000 lengths of a 25-metre swimming pool). He spends between six and 12 hours in the water by himself per day. Although every part of his training is done in isolation, he says he's OK with being by himself.

"The mental element is huge. It doesn't matter if there's a lifeguard at the pool or a kayak by my side in the ocean. Ultimately you're on your own," he said. "Then you start to wonder if you can, wonder if you're going to make it, and the physical ailments go from being simple aches and pains to, 'Oh my God my shoulder is falling apart' or pulled muscles [and] leg sprains. It's about keeping dramatic effects under wraps."

Hooper said he has a knack of being able to disappear when he's in the water. He describes it like driving somewhere and not remembering how you got there. One moment he's at the three-kilometre mark, the next he's got a couple of kilometres to go before he feeds and rests for lunch. His mental secret is a peculiar bag of distractions: studying arithmetic, reciting Shakespeare, having conversations with himself, solving real-life problems and even constructing story plotlines for his next book of fiction. He doesn't call it a contingency plan because Hooper believes it's hard to create one when he doesn't know what to expect in the ocean, but listening to tracks by Eminem, Swedish House Mafia and The Script seem to improve his physiological performance.

"Overcoming pain and loneliness, it's something I'm used to doing," he said. "It doesn't make it any easier, but in terms of coping in the Atlantic, if I run out of coping mechanisms in my head, I think I'll be looking to my support crew on the boat to lift me."

In an empty meeting room surrounded by yellow plastic chairs and white tables at the Toronto Pan Am Centre, Steph Horner explains how there are periods where her brain switches off and that's when she focuses on an upcoming feeding, where she'll replenish lost reserves, intake caffeine for an extra boost, rest and communicate with her coach. Anything to stop her mind from wandering off.

"Pool swimming is tough, but you can visualize it. Open water I'd say it's rough. You have to learn how to always adapt because you never really know what's going to happen. So you have to be able to take in things but not let them aggravate you," the 5'8" freestyler said.

"You have to almost imagine the worst that can happen, so that nothing can really phase you."