Online parenting groups have been abuzz recently over a simple photo. The image shows a glittering blue swimming pool, with nothing disturbing its appealing turquoise surface.
Empty chairs near the edge suggest there's nobody around - and it's only when a small section of the image is circled that it's revealed there's a child below the surface, swimming near the bottom of the pool.
The caption reveals that the child is wearing blue swimwear - making them impossible to spot.
The image was shared by an Australian Facebook group, CPR Kids, run by registered paediatric nurses. They warn that children should always wear brightly coloured swimwear, making them easy to spot and locate immediately underwater if they get into difficulties. They also pointed out that it's 'vital' to supervise children in water of any depth, and urged parents to learn CPR.
A page user called Michelle wrote, "Please everyone, if your kids have got grey or blue swim suits, throw them out now. I've just watched a 5 year old boy be rescued from the pool unconscious and not breathing. I didn't even see him at the bottom of the pool, he was wearing light grey swim shorts.
"After a few minutes of CPR, the amazing lifeguards got him breathing again and off in an ambulance, but this truly was a thing of every parents' nightmares...please check your kids' swimsuits."
Other parents shared their own stories of being unable to see their children in a pool, with one named Catharine writing, "don't swim in cloudy water, the pool filter needs to be checked and you should be able to see the bottom."
Watch: Swimming safety tips for parents and children
A life saver called Paddy warned, "anything other than fluoro will disappear underwater" and others advised wearing polarised sunglasses to make children easier to spot in shimmering water.
"Oh no!" One parent added, in response to the image, which has since been widely shared. "Definitely bright colours from now on!"
One website, Natural Parents Network quotes Laura, a mum who says "as a former competitive swimmer, lifeguard, swim coach, and Water Safety Instructor, I knew a lot about keeping kids safe in the pool. I knew my children would have swim lessons, and they have. I knew I would teach them about pool safety, like why they should always walk on the deck, only swim with a grown-up around, and listen to the lifeguards. (And they know and follow these rules.)
"But even though I knew a lot about keeping kids safe in the pool, one trick escaped me: brightly colored bathing suits.
"Although water is clear, it can appear blue due to the reflection from the sky or the colour of the bottom of the pool. Lifeguards, who sit above the water, may find it harder to see children at the bottom of the pool who are wearing blue or green bathing suits. Seconds matter, and being able to clearly see a swimmer in distress can mean the difference between life and death."
She advises choosing bright orange, read or neon swimsuits.
ROSPA, the Royal Society for the Prevention of Accidents, also has strong advice for parents taking children swimming, in or outdoors.
"Constant supervision of children whilst at the swimming pool is essential," they say. "Although drownings in pools are extremely rare, evidence suggests that children under the age of 11 are most at risk and toddlers are the most vulnerable. It is not sufficient to rely solely on the supervision of the lifeguard at the pool-side.
"Ensure that you are familiar with the pool environment, recognise particular hazards, like changes in depth and check out where the points of help are and the location of rescue equipment. Be particularly vigilant in 'leisure pools' where there may be a number of features within the pool, like flumes, fountains and waves."
They also point out that leaving kids to have fun, even for a few minutes, is unwise.
"If you are supervising more than one child, do not leave one child in the pool whilst taking the other into the changing rooms, unless you are confident of their swimming ability and maturity. Whether you need to be in the pool with the children you are supervising will depend on their age and swimming ability.
"Generally it is better to support non-swimmers by being in the pool with them. Younger children who are out of their depth in all, or most of, the pool will need physical support. Because supervision does need to be constant, recognise that you will not have the opportunity to swim and exercise yourself," they warn.
As swimming lessons and weekend family pool visits begin again, and we dream of holidays abroad come half term, now's a good time to invest in some hi-vis swimwear. It doesn't matter what style you pick - it's simply a case of the brighter the better, for very good reason.