Long before she dove inside icebergs and explored the world’s underwater caves, Jill Heinerth’s potential was almost cut short. She had a near-drowning experience at the age of 2.

Out of her mother’s sight at the cottage, she fell face-down into the water from the dock. Instead of panicking, she floated, an “ancient instinct” kicking in to hold her breath. She remembers the sun “shining in rainbows through the water.”

She was quickly snatched up by her mother, who was terrified. Heinerth herself was giggling, she recalled on CTV’s Your Morning.

“I guess water is my element,” she said. “Everybody can be a mermaid under water, this beautiful, graceful, weightless being.”

The Canadian underwater explorer is one of the world’s preeminent cave divers. She once dove inside an iceberg the size of Jamaica, something that had never been done before. Heinerth details her decades of diving into some of the least explored areas of the world in the new book , out now.

Though many would balk at the thought of being in an underwater cave, managing fear is part of her profession. Before an expedition she’ll consider what might kill her, run through scenarios and find solutions in advance, so she can enter the water “stress free.”

“When things go wrong, your heart wants to race, you want to start breathing quickly, your head wants to run away with thoughts and ideas. But that’s where part of the training is—to take a deep breath, turn off the emotions and just be pragmatic about dealing with really difficult situations.”

But fear isn’t really in her blood. “I don’t have a bit of claustrophobia in me,” she said. She credits some of that to having a gene variant known as DRD4-7R, sometimes called the “.” It’s a sensation-seeking, novelty-seeking genetic code that she believes drives her passion.

“It doesn’t mean I’m an adrenaline junkie. It’s more like maybe in my ancestry we were the hunter gatherers as opposed to the ones farming at home,” she said. “That has fueled my sense of adventure.”