It's been called the Holy Grail of marathon swimming and it starts here, a marina in Havana where swimmers have tried - but failed - to set off unassisted from Cuba to the U.S.
On Wednesday, 28-year-old Australian Chloe McCardel took a shot at the grail, by trying to become the first person to make the swim WITHOUT a protective shark cage, which helps cut through the water.
REPORTER OFF CAMERA: "How are you feeling?
MCCARDEL: "Very well, thank you.
The sea looks calm now, but difficult currents stymied earlier efforts by others.
This time, the swimmer has lots of help - an army of 50 to help her navigate, and an underwater electromagnetic field to repel sharks.
McCardel is making the swim for cancer research and to improve U.S.-Cuban relations.
If all goes well, she'll reach Key West in about 60 hours on Friday night.
