A 17-year-old Toronto-area teen who successfully retraced swimmer Marilyn Bell's route across Lake Ontario said the marathon swim was tough, especially at night.

Just shy of the previous record set by a former Liberal MPP, Rebekah Boscariol of Markham emerged from the water after 15 hours, 33 minutes and 15 seconds.

"(The) night was definitely hard because I was alone and it was cold," Boscariol told CTV Toronto.

Boscariol was greeted by friends and family as she surfaced the water at Marilyn Bell Park in Toronto.

"I was really happy that I was done and thankful that it's over. And I just can't believe that I just actually did it," a visibly tired but elated Boscariol told a reporter.

Just a day earlier, Boscariol hit the water just after 8:30 p.m from Niagara-On-The-Lake.

The goal was to raise $20,000 for Toronto's Hospital For Sick Children, where her younger sister, Sophia, had surgery. Sophia, 4, was born with a hole in her heart, which was repaired by doctors of The Cardiac Care Unit at Sick Kids.

"She was actually only in there for a day. We were really lucky with that because she didn't have to have open heart surgery," Boscariol told CTV Toronto on Saturday after her swim.

To train for the 52 kilometre challenge, Boscariol has been swimming laps 14 hours a week, in addition to dry land training. The teen also put on 10 pounds of body mass, which her nutritionist said will help her maintain energy and warmth in the frigid waters.

In a July 2 blog post, Boscariol said she was enjoying the process because she could "basically eat whatever I want, whenever I want :)"

"So my nutritionist, Lauren Jawno, told me today that I would have to gain about 12 lbs for the swim … We decided that the best way to do this would be the nutritious way, as in eating frozen yogurt instead of ice cream and real chocolate instead of milk chocolate," Boscariol wrote.

Boscariol, who has been swimming competitively for nine years, was accompanied by four sailboats, 18 volunteers and rescue personnel.

To refuel, Boscariol broke every half hour in the water.

"I drink a mixture of e Load carb powder and flavour. That's basically my main drink and you can also have baby crackers and arrowroot," Boscariol told CTV Toronto hours before her swim.

But despite the precautions and training, Boscariol still faced many challenges throughout her treks across the lake, including psychological and physical obstacles.

Dr. Greg Bell, who has himself accompanied another swimmer across Lake Ontario, said the cold is a major hurdle.

"Just staying warm is going to be a challenge for her because she's going to be exercising. Heat's going to be coming right out of her muscles through her skin and out into the water, literally being sucked out of her," Bell told CTV Toronto.

Boscariol is the eldest of six children and is a student at St. Augustine Catholic High School in Markham. Donations can be made at http://www.swimthedistance.com

With files from The Canadian Press and reports from CTV Toronto's Pauline Chan and Colin D'Mello