It takes only seconds, with devastating consequences.
It's something that Catherine Giudici Lowe explained on social media about her two-year-old son, Samuel and the deep end of his grandparent's pool.
Taking to Instagram, the mum-of-two recounted the heart-stopping moment the tot accidentally walked into the deep end of the swimming pool.
"WARNING: Sappy Mom Content. One week after Isaiah was born, Samuel mistakenly walked into the deep end of his grandparents’ pool and it was possibly the scariest moment of my life," she said.
However, the fright of her life meant that she and husband, Sean Lowe decided to put Samuel into swimming lessons.
"Sean and I were watching his every move so we acted quickly to get him out (I was much more traumatized than he was), but we immediately put him into swim lessons and made sure he always has floaties on."
"Today was his LAST DAY of swim lessons and now he can swim to the side like a champ! I’m so proud of this big guy even though he cried through almost every single class. Watch out world, this little shark is a-swimmin!" concluded the proud mum.
The couples second child, Isaiah Hendrix was born on May 18.
If the 32-year-old's Instagram is anything to go by, it looks like Samuel is now a natural in the water.