Ms Barwick was then confused as to why her legs were not working.
The 46-year-old was then flown to a Mackay hospital where she was fighting for life after suffering leg and torso injuries.
Ms Barwick was the first of several shark attack victims that followed, including 12-year-old Hannah Papps, who was bitten less than 24 hours after her in the same harbour.
A Victorian doctor lost his life two months later when he was fatally mauled by a shark in the Whitsundays.
Ms Barwick told The Advocate News she had not seen anything in the water to cause concern before the attack.
«And I’d jumped, dived into the water there literally thousands of times before,» she said.
Ms Barwick said she found it difficult to describe what happened next but the shark immediately «slammed» into her.
«I was really scared. I think it was a fight-or-flight moment because I just swam straight back to the boat and I got out of the water and my friend was still in the water,» she said.
«That makes me a little bit sad that I knew that there was a shark in the water and my survival instinct was so strong that I got out first.»
Five months on, Ms Barwick has returned to her role as operations manager at Family Based Care Tasmania.
She continued to receive regular physiotherapy as part of her rehabilitation but was left with lifelong disabilities as a result of the shark bite.
Family Based Care Tasmania chief executive Douglass Doherty said he was glad the team could assist Ms Barwick during her recovery but could vividly recall hearing her story.
«It’s difficult. We all assume the friends are going to be with us for the rest of lives but when this sort of tragedy strikes, it makes us realise how fragile human life is and that we really should take the time to appreciate them,» he said.
«Justine is a very strong person and a fighter.»
Mr Doherty said there was a gap in the business while Ms Barwick was away from work.
«It’s with great relief that I welcome Justine back to work, her knowledge and expertise is tremendous,» he said.
Ms Barwick said she was overwhelmed by the community support received for her family and her workplace during her recovery.
She said she was «incredibly lucky to be alive» and hoped to return to as normal a life as possible.
-with Lachlan Bennett
Jocelyn Garcia is a journalist at the Brisbane Times, covering breaking news.