Glossary
Shallow water blackout
Passing out underwater after hyperventilating or holding your breath too long. It can drown even strong swimmers.
Shallow water blackout, also called hypoxic blackout, is when a swimmer passes out underwater after hyperventilating (breathing fast and deep) or holding their breath for a long time. It can happen to strong, confident swimmers, often during breath-holding games or underwater distance contests, and it can lead to drowning within moments.
The CDC (opens in a new tab) is direct: do not hyperventilate before swimming underwater, and do not try to hold your breath underwater for long periods, because this can cause you to pass out and drown. The American Red Cross (opens in a new tab) lists understanding the dangers of hyperventilation and hypoxic blackout as part of basic water safety.
Rules that help:
- No breath-holding contests or repeated underwater laps.
- Never practice breath-holding alone.
- Lifeguards and Water Watchers should treat a still swimmer on the bottom as an emergency.
See supervising confident swimmers and water safety for teens.
What you can do today: tell the swimmers in your family that breath-holding games are off the list, and explain why.