Before she reclaimed her dream and completed the swim from Cuba to Florida, Diana Nyad built her marathon swimming resume in the waters of Lake Ontario.

It was Aug. 30, 1974 when she became the first person to cross Lake Ontario from north to south. But her bid to become the first person to complete a double-crossing of the Great Lake ended after 20 hours and 30 minutes when she was removed unconscious from the water.

It was 12 years later when Vicki Keith would become the first person to complete a double-crossing of Lake Ontario. Keith crossed Lake Ontario five times, including 25 years ago when she took on the feat of swimming all five of the Great Lakes in one summer.

Nyad, 64, finally accomplished the swim of her lifetime on Sept. 2 when she completed a 110.4-mile trip from Cuba to Key West in 52 hours, 54 minutes. It was her fifth attempt at the swim and 35 years after her first attempt, as a 28-year old in 1978.

When news hit that Nyad had finally accomplished the swim, Keith shared in the celebration.

“I am so happy for her,” said Keith from her home in Kingston, Ont., where she works as a swim coach. “I can’t imagine having that eating at you, in the back of your mind all those years. There was something telling her to do it, and for her to get it done after all those years is just wonderful.”

Keith knows all about the physical and mental work it takes to cross a body of water. Not only did she conquer the Great Lakes, but in 1989 she completed the first crossing of the English Channel using the butterfly stroke and also crossed the Catalina Channel.

She also knows about balancing the best waters to suit your performance while battling the elements that come with weather conditions.

“I think one of the things Diana Nyad really struggled with was she wanted to swim when the strait was its warmest,” Keith said. “She doesn’t do as well in cold water. But as she waited for the warm water, that brought the challenge of the jellyfish. And it’s hurricane season. You’re trying to balance what challenge fits you best with the conditions.”

And that brings us back to Lake Ontario that has been ranked as one of the toughest open water swims in the world by Open Water Swimming.

The shores along Western New York and Southern Ontario provide some of the most challenging conditions for open water and the region has a rich history for marathon swimming.

Marilyn Bell was the first person to successfully cross Lake Ontario, starting in Youngstown and finishing near the Canadian National Exhibition in Toronto. She was 16 when she completed the feat in 1954.

The most popular route is to travel south to north, beginning at Niagara-on-the-Lake and finishing where Bell did, the site now known as Marilyn Bell Park.

There are 65 recognized completed crossings of Lake Ontario by Solo Swims, most of them using the traditional route that comes in at 31.4 miles.

What makes Lake Ontario so difficult to cross?

“The change of weather for one,” Keith said. “People get in and the water is glass smooth. The water temperature when you start off could be 75 degrees but by the time you get near Toronto, it’s 50 or 55 degrees.

“The wind direction will impact the conditions because where the Niagara River enters Lake Ontario, the current drives to the bottom of the lake and you have surges in Toronto. That’s what created the Toronto Island. And because the current is coming from the bottom of the lake, it’s bringing the cold water up.”

There’s also the distance factor — 32 miles is longer than the English Channel or Catalina Channel swims.

But even with the obstacles, Keith is starting to see more people interested in marathon swimming. Open water swimming became on Olympic sport in 2008 and features a 10K swim for both men and women, raising the profile of the sport.

And while triathlon swimming has some key differences it has helped introduce a new group of athletes to open water swimming.

“You are seeing more people saying, ‘That’s something I can do,’ ” Keith said. “I think there is a relationship with triathlon which is just a great sport and as it grows it gets more people looking at marathon swims.”

And the key to a successful swim?

“You have to be physically fit. You have to train physically to take on the challenge,” Keith said. “But the part people forget is the mental training. You will emotionally break down in a marathon swim. You will go through ups and downs and you have to break down into smaller goals.

“People ask me what percentage is physical and what percentage is mental. I say it’s 100 percent physical and 100 percent mental. You can’t divide the two. But people train for the physical and forget to train for the mental part of it.”