Anna Wardley, 40, will attempt to swim a total of 215 km between Menorca and mainland Spain without a wetsuit.
She is due to embark on the first stage of the challenge on Wednesday with a 37-kilometre swim between Menorca and Mallorca in support of local charity Joves Navegants.
But during months of intense training, she has already had to overcome challenges.
"Just a week ago I was hospitalized due to a severe reaction to jellyfish stings sustained during my training, but nothing can stop me now," she said in a statement to The Local.
"I have trained for this for months. My mind, heart and soul are ready for this moment. I just hope there aren't too many jellyfish out there."
Wardley has already swam around the Isle of White. Photo: Sofia Winghamre
Wardley, who divides her time between homes in Gosport, UK and Colonia Sant Jordi on Mallorca, will be accompanied in the water by a support boat and crew and who will hand her specially prepared food to sustain her energy levels.
Her chosen provisions include "rice pudding, chocolate soya pudding, Percy Pig jelly sweets and fresh mango, strawberries and Kiwi fruit," Wardley explained.
After this week's crossing between Menorca and Mallorca, she will swim on to Ibiza and from there to Dénia on mainland Spain.
If successful, Wardley will become the first person to succeed in the Balearic Island Challenge, a mission she has undertaken to raise money for three charities: Marine Inspirations, Joves Navegants and the Marine Animal Rescue Project.