Bárbara Hernández Secures Her Fourth Guinness World Record with the Longest Swim in History in Puerto Natales

This new record marks the longest distance ever swum by a woman in the world in water temperatures below 5º Celsius. On August 30, the “Ice Mermaid” achieved her fourth Guinness World Record by swimming 3.84 kilometers in the Señoret Channel, facing extreme conditions of 4.5ºC water temperature and 0ºC air temperature, just one month after her historic double crossing of the English Channel.

Puerto Natales, September 2, 2025 – It’s official. Bárbara Hernández is now the Chilean woman with the most Guinness World Records. Today, the Guinness World Records Association officially recognized the latest feat of the extreme swimmer in Puerto Natales: the longest distance ever swum by a woman in water temperatures below 5ºC.

The “Ice Mermaid” accomplished this on Saturday, August 30, swimming 3.84 kilometers in the Señoret Channel in Puerto Natales, facing the lowest temperatures ever recorded in this type of challenge: 4.5ºC water temperature and 0ºC air temperature.

Without a wetsuit or insulating fat layers, and true to her style as an extreme swimmer, Bárbara completed the feat in 1 hour, 6 minutes, and 15 seconds, surpassing both the distance and time of the previous women’s world record set in Poland this past March. This achievement came just one month after her historic double crossing of the English Channel, where she swam for more than 27 continuous hours.

The swim began at 9:44 a.m. (Magallanes Time: 8:44 a.m.). Within minutes, Bárbara’s body temperature began to drop dangerously. Upon leaving the water, she was diagnosed with hypothermia, with a body temperature of just 31ºC, while the wind chill during the swim reached –3ºC.

“It was one of the toughest swims of my life. I don’t remember the final part due to the hypothermia; I knew that if I stopped, I might lose consciousness. But quitting was not an option,” said the Ice Mermaid at the end of the challenge. Despite the harsh conditions, Bárbara thanked her medical and logistics team: “We made it thanks to every person who was on land, in the water, and cheering from start to finish. This swim belongs to all of us.

The Journey of a World Champion

Bárbara Hernández already held three Guinness World Records for her extreme water feats.

• The first came in 2022 at Cape Horn for the fastest mile swum in 15 minutes and 3 seconds and for the longest distance swum there: 5.5 kilometers.
• Her second and third records were achieved in Antarctica in 2023, for the longest swim in polar regions and for being the only woman to complete 2.5 kilometers there, swimming in 2.23ºC waters for 45 minutes and 30 seconds.

Medical Safety and Recovery Protocol

Cardiologist Nicolás Bunster and nurse Camila Carvajal led the medical protocol with minute-by-minute monitoring of temperature and vital signs. Upon leaving the water, Bárbara’s body temperature had dropped to 31ºC.

The recovery process took place in two stages:

1. First stage: In the recovery tent, immediately after the swim, lasting 1 hour and 40 minutes, focused on strict vital signs monitoring and controlled rewarming using non-invasive methods guided by core temperature.
2. Second stage: Lasting several more hours, aimed at full normothermia restoration.

“To measure her temperature, we used a core temperature monitoring system that records readings every minute through a capsule (eCelsius) that the swimmer swallows one hour before the swim, remaining in the digestive tract and transmitting real-time core temperature data,” explained the cardiologist.

This system allows for a better understanding of the physiological processes happening in real-time and enables precise adjustments during rewarming, avoiding invasive procedures for temperature measurement and recovery. Continuous electrocardiographic and hemodynamic monitoring was also carried out throughout the recovery process.