Here are six things you may not have known - but should - about such tragedies:
"The Baywatch syndrome," says Benjamin Taitsch, deputy chairman of the Bavarian Water Rescue Service in Germany. A reference to the former American TV series about lifeguards that became popular around the world, it's the common assumption - abetted by portrayals on "Baywatch" - that someone who's drowning will splash about and cry out loudly for help.
"In fact, it usually happens very, very quietly," Taitsch says.
Often the person no longer has the strength to frantically wave their arms. "They have other things to do than draw attention to themselves - they're fighting for their life," remarks Philipp Pijl, head of the deployment team at the federal office of the German Lifesaving Society (DLRG).
Another common misconception, says Pijl, is that most drowning victims are non-swimmers. "Whether the person can swim or not is hardly the only factor," he says. Statistics - at least in Germany - show that if you thought most victims were children and adolescents, you'd be wrong.
"They're mostly middle-aged or older men," points out Pijl, explaining that carelessness, alcohol consumption or sudden circulatory insufficiency can put even experienced swimmers in peril.
It could be underestimating a river current's strength, swimming too far from shore in an intoxicated state, or a child slipping and falling face-first into the water. Whatever the circumstances of a drowning, death is due to a lack of oxygen caused by being unable to breathe under water.
All of the body's organs - primarily the brain - can only function when they're adequately supplied with oxygen.
Using the example of a water sports enthusiast on a stand-up paddleboard (SUP) in summer, Philipp Wolf, a physician for the Bavarian Water Rescue Service, describes how a drowning might occur:
It's hot, and the young man's body is heated up. "If he unexpectedly falls into the water, he experiences a cold shock, even though the water may not be particularly cold," Wolf says.
In a kind of paralysis, the paddleboarder reflexively inhales deeply with a gasp, as one does when plunging into an ice bath after a sauna session. "This allows water to get to the glottis [the thin opening between the vocal cords at the top of the larynx, or voice box] and vocal cords, which then close."
Called laryngospasm, this seizing up of the vocal cords is a protective reflex that seals off the airway inlet at the throat and prevents water from entering the lungs. But it makes the paddleboarder unable to cry out. He panics.
"He can't breathe, and doesn't have any air left," Wolf goes on. Deprived of oxygen, the man loses consciousness after a short while and goes under. "In cases like this, generally no water is found in the victim's lungs - it's a 'dry' drowning."
In other cases, lots of water enters the lungs, for example if the person has a medical emergency such as a heart attack while swimming. "If it's a mild heart attack, they may still be able to swim, and panic. If it's severe, they're under water in just a few seconds," says Pijl.
While it's not very easy for a non-expert to have an eye for this, Taitsch points to some possible signs of a critical situation: "The person's swimming motions are desultory. They're still there in spirit, but the person's head quickly goes under water, making breathing impossible."
Another possible sign, adds Pijl, is when someone's swimming motions suddenly become much faster or slower.
Children are different. "You typically don't see a panic reaction from them. They become rigid and simply go under," Wolf says. Sometimes mere seconds separate happy play on the shore and life-threatening immersion, which is why parents should never let their children play at waterside without supervision.
The earlier a drowning person is pulled from the water, the better their chances of surviving and not suffering permanent injury. So "as soon as you have the feeling that something's amiss, don't hestitate to call the local emergency number," Taitsch says.
It's important to state your precise location and remember where the person went under. And if a manned lifeguard station is nearby, inform the lifeguard(s).
If no professional life-savers are yet on site, you've got to gauge what actions you're capable of yourself. Maybe a lifebelt is at hand, or you could paddle out to the spot on an SUP so that arriving rescuers can see where it is. Or you might be a good enough swimmer to try to bring the person to safety yourself.
"It's important that you only do what you're confident in doing," emphasizes Taitsch. Otherwise you could easily endanger your own life, because a drowning person in panic clings for dear life to whatever - or whomever - offers hope of rescue.
"If the person is still responsive, as you swim over to them you can tell them you'll be there straightaway to help," advises Pijl. This can have a calming effect.
A standard guideline is to swim to a drowning person from behind so that they don't pull you under water. Pijl rejects it though. "If the person is still conscious, they'll panic even more if they're simply grabbed from behind."
He therefore recommends approaching head-on at a safe distance at first, and explaining you're about to swim over from behind and grasp them behind their arms.
There are other ways to help a drowning person - and keep your distance. Wolf recommends tossing a sweater, jacket, large stick or bath towel towards them.
"The object doesn't have to be able to buoy the person," he says. "But they can grab onto it, and you'll have a better chance of pulling them somewhere - if only to swallow water where you can stand."
If the person is unconscious, a knowledge of emergency first aid is necessary - more specifically, chest compressions to enable the oxygen remaining in the person's blood to circulate throughout their body.
Ideally this should be combined with mouth-to-nose or mouth-to-mouth resuscitation. Wolf advises first artificially ventilating the person five times: "When no oxygen remains in the person's lungs, chest compressions alone are insufficient. Oxygen has to get into their lungs somehow."
You should continue your resuscitation efforts until professional rescuers arrive and take over.
