The tragedy of four-year-old Mia's death highlights what so many of us don't know about drowning.

Four-year-old Mia Harrison was meant to start big school next year.

Last Tuesday, she went to her Kindergarten orientation day. Her mother Mekaela shared a photo of a smiling little girl, wearing a pink hat, matching pink pants, a long-sleeved shirt with a gold heart, and tiny purple sand shoes. In another photo, she sits in the classroom holding a purple pencil, smiling excitedly at the people around her.

For Halloween just last week, she dressed as a witch.

But on Saturday, Mia went to Orange Aquatic Centre with a group of family and friends, and would never return home. In a “matter of seconds,” the little girl, who could not yet swim, either fell or was knocked into the water. She was found motionless at the bottom of the pool, and while lifeguards and family members desperately attempted to revive her, Mia was pronounced dead upon arrival at Orange Base Hospital.

Speaking to The Daily Telegraph on Sunday, Mekaela Harrison described the pool as “very crowded with lots of children and adults around”.

“Accidents happen. Nobody is to blame. I would not wish any other parent to go through this, it’s impossible to understand how horrific it is,” she said.

The haunting story of Mia's death - in a public pool with adults present - highlights what so many of us don't know about drowning.

That is, that children and adults can and do drown at crowded public pools, at a similar rate to backyard pools. But for a long time, our statistics have been skewed.

While rivers, lakes, coastal waters and home pools are more deadly than public swimming pools, the rate of 'non-fatal drowning' is public pools is roughly the same as home pools. Non-fatal drowning is the medical term for the event in which a person technically drowns but is brought back to life. The person is underwater for long enough to require serious resuscitation attempts to survive, and can suffer long-term injuries such as brain damage. These swimmers are often not included in drowning statistics, despite having gone unnoticed by those around them for a near-fatal period of time.

In February 2014, 23-year-old Paul Daniel Rayudu was found at the bottom of a 50m public pool in Greensborough, Victoria. Just as his motionless body was pulled to the surface, bystanders heard a cry: "Oh my God, there’s another one in the pool!"

The man's girlfriend, Virajitha Kelangi, was also face down and in a serious condition. Rayudu died six days later, and Kelangi was discharged from hospital the day after her partner's death.

At the time, the community wanted answers to some serious questions about how two adults - one of them partially clothed - could be underwater for so long without anyone noticing.

In a report by The Age, it is argued that not only are drownings "quick and silent," a far cry from the violent thrashing we typically associate with drowning, the crowded environment of a public pool can lead people to misjudge the level of supervision. Lifeguards are not nearly as skilled at spotting a person in distress as we think.

The Age sites a US study about lifeguarding techniques, which warned of "inattentional blindness" - a psychological phenomenon in which people fail to notice an unexpected stimulus in plain sight.

This flaw is exemplified by a well-known experiment called The Invisible Gorilla, whereby people were asked to watch a video and count how many times three basketball players wearing white shirts passed a ball. At around the 30 second mark, a woman dressed in a gorilla costume appeared. Approximately half the viewers could not recall seeing her.

Human attention is far from perfect, and in a crowded, public environment, we naturally assume the people around us are safe.

Fatalities in public pools are rare, and that's likely because once a drowned person is spotted, staff at these facilities have the resources and skills to bring them back. But both children and adults can and do drown at public pools, and four-year-old Mia Harrison death is a disturbing reminder of that.