Veteran long-distance swimmer Diana Nyad has begun her fourth - and likely final - attempt to swim the 103-mile journey from Cuba to Florida without a shark cage.
Instead of a cage, it's hoped that equipment emitting a mild electric current into the water will keep the sharks at bay.
The 62-year-old American set off by diving into the Florida Straits on Saturday with a shout of "courage".
She hopes to land somewhere in the Florida Keys early on Tuesday - the day before her 63rd birthday.
Ms Nyad told reporters beforehand, "I'm really excited. I respect this. I know how difficult it is. There's a reason no one's ever done it, but I'm prepared ... I may suffer some, but I'm prepared for that, too".