In a footage of the tragedy, the woman had her back turned while her son desperately fought to stay above the water in the background.
She was completely oblivious to what was going on as she seemingly searched for the four-year-old after finishing with her phone.
As the woman walked off, she had no idea that her son was seconds from death and struggling for his life a short distance away.
The incident which happened in China, has been shared hundreds of times on Twitter by people raising awareness of the risks of leaving children unsupervised in water.
The Child Accident Prevention Trust warns that babies and children can “drown silently” in as little as five centimetres of water.
It added: “In the last six years, 30 children under 10 have drowned in a hotel or villa pool abroad. This usually happens when they wander away from their parents and fall into the pool.”