Jillian Searle and her family are now safe in Perth
She had her two young children with her, but realised she would only survive if she let go of one of them.
"I knew that if I held on to both, we would all die," she told reporters. "I just thought I'd better let go of the one that's the eldest."
Fortunately all three survived, and are now back in their home city of Perth.
Moments before the tsunami hit, the Searle family had been enjoying breakfast near their hotel pool.
Mrs Searle's husband had just gone back into the hotel when water engulfed the area, and she found herself clinging onto her two sons, desperate to keep hold of them.
Still clutching her two-year-old son, Blake, she appealed to a woman nearby to grab hold of five-year-old Lachie - who cannot swim.
Although the other woman tried to hold on, she was forced to let go and he slipped into the water.
The boys' father, Brad, watched the scene helplessly from the balcony of their first-floor hotel room.
He found his wife and younger son soon after the water receded, and the family then went in search of Lachie.
"I was screaming, trying to find him, and we thought he was dead," Mrs Searle said.
Lachie was found two hours later, having been discovered by a security guard clinging to a door to keep his head above water.
"We are just so lucky to walk away with the small children I've got, one of whom can't even swim and is petrified of water - even the pool at home - and one who is a little baby," said Mrs Searle.
"I just can't believe they are still here."===============================================
Boy's Plea: 'Don't Let Go of Me Mummy'
The churning waves were just too overwhelming and she knew she couldn’t keep both of her sons afloat.
Keeping a firm grip of her younger son, she shook off the grasp of her older boy, whose fingers were entwined in her other hand.
“I could feel him squeezing me,” Mrs Searle said. “And he said to me, ’Don’t let go of me mummy.”’
In an interview with Australia’s Nine television network, Mrs Searle gave details of the horrifying choice she made when the Asian tsunami barrelled into the resort island of Phuket, Thailand, where she and her family were holidaying.
She said she noticed a young woman clinging to a nearby post and begged her to take hold of five-year-old Lachie as she held on to two-year-old Blake.
But as the mother looked back at her son, who had not yet learned to swim, she thought she would never set eyes on him again.
Her husband, Bradley, had been watching from the hotel’s second-floor balcony. He tried to rush out to help his wife, but the rising water blocked the way.
“The water level was so high you couldn’t open the doors,” he told the TV network. “Then I found a bar on the ground and I tried to get that into the door and lever the door open.”
Once he reached the first floor, a second massive wave crashed over the beach, forcing him to clamber to safety on top of a drinks bar.
The father, mother and youngest son were reunited soon afterward. But no sign of Lachie.
Frantic, Mrs Searle told her husband: “You have to find him because I let go of him. I gave him to somebody else, and I let go of him ... and there is no possible way I can live my life knowing that I took his hand off mine.”
For two hours, the Searles searched.
Their calls were drowned out by car alarms set off when wave-tossed vehicles smashed against buildings.
Finally, they found Lachie with a Thai policeman. The boy had survived by clinging onto a hotel room door.
“I cried for mom for a long time and then I was quiet,” Lachie later told his father.
With mud and water marks up to his ears, his first words to his father were: “My hands are all dirty and I need to wash my clothes.”
Mrs Searle explained her decision in a separate interview with Sky News.
“I knew I had to let go of one of them, and I just thought I’d better let go of the one that’s the oldest,” she said.
She told Sky News that the woman she’d pleaded with to save her son had picked up the child but couldn’t hold on.