Swimmer Diana Nyad believes that age is just a number. She wants others to start believing it too. That’s why today at age 61 Nyad is attempting to set a new world record for open water swimming.

She will do so during a harrowing, 103-mile swim from Cuba to Florida without the aid of a shark cage. Diana began her journey late Sunday evening, entering the waters in Havana at about 7:45 Eastern Time.

The plunge marked the end of a difficult challenge for Nyad and the beginning of another altogether. Last year she spent months trying to convince officials in both the United States and Cuba to allow the attempt before being forced to call it off late in the season as temperatures dropped.

Though travel restrictions between the contries have shown signs of easing up, diplomatic tensions still exist and can easily complicate an undertaking like this. Diana recommitted herself to training and her lobbying efforts finally paid off earlier this year when she received permission from both governments to make the journey.

Nyad has now been swimming for more than 15 hours, taking small breaks to keep up with her caloric intake. She will burn tens of thousands of calories during the swim, according to doctors.

She is being followed by a small flotilla of handlers, doctors, and reporters. You can track her progress over at CNN.