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The Dangers of Swimming Underwater – Shallow Water Blackout

Swimming Underwater can be a lot of fun. But did you know that it can have dire or even life-threatening consequences? Read more below.

Let’s be honest, as a child, everyone has at least once played the game with his friends about who could hold his breath underwater for the longest time or who could swim underwater the farthest.

While these activities may look like harmless children’s games, they are in fact dangerous because they can at first lead to shallow water blackout and subsequently to drowning.

A drowning man
Swimming Underwater can have dire consequences.

Shallow Water Blackout

Shallow Water Blackout happens when a swimmer or diver faints in shallow water, which is less than 16 feet (5 meters) deep.

Typically the victim hyperventilates before diving or swimming underwater, then dives or swims while holding her breath.

This leads to fainting underwater due to low oxygen levels in the bloodstream.

Why does this happen? In fact, the urge to breathe is driven by the level of CO2 (carbon dioxide) in the bloodstream.

However, if you hyperventilate, the CO2 is flushed from the bloodstream to a low level.

The urge to breathe will then set in much later than if you didn’t hyperventilate beforehand.

So if you do hyperventilate before you dive or swim underwater, what can happen is that the oxygen stored in the body is consumed before the level of CO2 in the bloodstream rises enough to trigger the urge to breathe.

You then blackout without any warning signs.

What makes this problem worse is that from the water surface, it often looks like there isn’t any problem.

The victim doesn’t make any warning signs or may even still be moving unconsciously.


As we have seen, diving or swimming underwater while holding your breath is dangerous, especially if you do hyperventilate before.

This explains why many public swimming pools forbid these activities.

Sadly, the general population is not yet well aware of this danger and still needs to be educated.

It is best to avoid these activities at all. However, there are cases where you need to dive or swim underwater while holding your breath, for example, to pass specific certifications.

In that case, you should always practice under the supervision of a lifeguard or friend that knows CPR (Cardiopulmonary resuscitation) and avoid hyperventilation before you dive or swim underwater.

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