The case of a young boy who kept smiling at his mother as he nearly drowned has raised awareness that people near death in the water can be silent and barely moving.

Chris Hicks' five-year-old son smiled at her, but said nothing, as he bobbed up and down in a pool at a friend's house in Wellington. Fortunately someone did realise the danger, jumped into the pool and pulled the boy out in time.

Hicks recounted the events of 17 years ago in a popular reader report on Stuff.

She recalled how her son seemed to be ignoring her as she tried to get him out of the water. "He kept smiling although it was a frozen smile. He never spoke a word."

Many commentators on the article were surprised a person could drown so quietly.

WaterSafe Auckland business manager Teresa Stanley said many people did seem to have a misunderstanding about all the signs that could indicate drowning.

"We've been brought up expecting there to be screaming and splashing and what not, and often there isn't," she said.

While she was unaware of any cases where a parent had watched, mistakenly thinking a child was okay, as the youngster drowned, she did know of cases where adults had not recognised for some time that a child was drowning and reacted later than they should have.

Constant education was needed to ensure people were aware of all the risks in water, Stanley said.

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One reader of Hicks's article recalled getting into trouble at a busy swimming hole at the age of 10.

"I could not raise either arm, or call out. I kept going under, and just could not move sideways. I was looking straight at one of my friends sitting on the bank, who did not notice anything wrong. I was lucky a man suddenly realised I was in trouble and jumped in and got me out," the reader said in a comment.

Water Safety New Zealand chief executive Matt Claridge doubted there would be many cases where people drowned without doing something that indicated they were in trouble beforehand.

"Unless you're knocked out, everyone in a bit of difficulty will be flailing to a degree," he said.

Often if someone was in trouble in the water their movements would look as if they were trying to climb a ladder.

A description of what drowning looks like is included in an article by former US Coast Guard member Mario Vittone, based on work by US drowning researcher Francesco Pia.

The article, under the headline "drowning doesn't look like drowning" draws a distinction between what it refers to as the instinctive drowning response, and a person in aquatic distress who may well be yelling for help and thrashing about.

While a person in distress is in trouble, they can still help with their rescue, Vittone said. With the instinctive drowning response people were almost always unable to call for help and could not wave.

This is how Pia described the instinctive response in the US Coast Guard's On Scene magazine:

1. Except in rare circumstances, drowning people are physiologically unable to call out for help. The respiratory system was designed for breathing. Speech is the secondary or overlaid function. Breathing must be fulfilled before speech occurs.

2. Drowning people's mouths alternately sink below and reappear above the surface of the water. The mouths of drowning people are not above the surface of the water long enough for them to exhale, inhale, and call out for help. When drowning people's mouths are above the surface, they exhale and inhale quickly as their mouths start to sink below the surface of the water.

3. Drowning people cannot wave for help. Nature instinctively forces them to extend their arms laterally and press down on the water's surface. Pressing down on the surface of the water permits drowning people to leverage their bodies so they can lift their mouths out of the water to breathe.

4. Throughout the instinctive drowning response, drowning people cannot voluntarily control their arm movements. Physiologically, drowning people who are struggling on the surface of the water cannot stop drowning and perform voluntary movements such as waving for help, moving toward a rescuer, or reaching out for a piece of rescue equipment.

5. From beginning to end of the instinctive drowning response people's bodies remain upright in the water, with no evidence of a supporting kick. Unless rescued by a trained lifeguard, these drowning people can only struggle on the surface of the water from 20 to 60 seconds before submersion occurs.