American endurance swimmer Diana Nyad is attempting to become the first person to swim between Havana, Cuba and the Florida Keys without a shark cage.

Nyad began her 166-kilometer swim across the Florida Straits Sunday evening.

Nyad called the swim a “symbolic moment” for increasing understanding between the United States and Cuba.

The marathon swim is expected to last 60-hours and has been a lifelong dream of the 61-year old American swimmer. Nyad is accompanied by a support team travelling in boats.

To be successful in the crossing, Nyad will have to complete the swim without a wetsuit or special equipment. Divers will be nearby to discourage sharks.

Nyad plans to stop every 45 minutes for a 20-second hydration break. Every 90 minutes she is scheduled to stop for a two minute rest and a snack. At no time can she touch the support boat or be assisted by her team.

Two days into the swim Nyad will need to ward off hypothermia by drinking warmed drinks. Despite water temperatures averaging 30 to 31 degrees Celsius hypothermia becomes a possibility after so many hours at sea.

Nyad attempted this crossing as a 28-year old in 1978, inside a shark cage. Strong seas ended the swim after 42-hours.