Annaleise Carr said in a Friday morning interview with CBC News that she and her team were as prepared as they can be — but there's always the unknown factor of the weather.
High winds can whip up waves, making it much more difficult to swim.
"I think the hardest thing for me is going to be the weather," she said.
In fact, she had intended to attempt the swim on Friday, but her team decided to push back her attempt by 24 hours because of predicted windy weather.
Carr stepped into the water at Niagara-on-the-Lake at 6:17 p.m. ET on Saturday, and if everything goes as planned she'll arrive at Marilyn Bell Park in Toronto near mid-day Sunday.
A competitive swimmer since the age of four, the teen said she got the idea of swimming the lake after visiting Camp Trillium — a camp for children with cancer.
"I was going to volunteer [at Camp Trillium] but you have to be 18, so I was thinking of ways to help and I remembered that one of the guys that did a 10-kilometre [swim] with me jokingly said that I should swim across the lake," she said in an interview with CBC News.
She's has raised nearly $30,000 so far.
If she makes the 52-kilometre crossing she'll become the youngest to accomplish the feat.
Carr says she's been doing lots of long distance swims to prepare along with other training specifically geared to the lake crossing. "I've been doing some night swimming, because most of it will actually be during the night."
She said she's also "practised feeding because I actually have to feed while I'm in the water."