The Open-Water Safety Update: When Breathlessness Means Stop Swimming

You should never swim through unexplained breathing trouble.

You expect heavy breathing during a hard open-water effort. You might also expect a brief gasp when you enter cold water. But when you develop unusual breathlessness, a persistent cough, or chest tightness during a swim, you need an exit plan, not a tougher mindset.

Your safety briefing should include swimming-induced pulmonary oedema, or SIPE: a condition in which fluid enters your lungs during swimming. You might also hear the broader term immersion pulmonary oedema, which covers similar episodes during other water activities. You can experience it without inhaling water, and your fitness does not rule it out.

Update your understanding of breathing trouble in the water

You may associate swimming emergencies with swallowing water, panic, or exhaustion. SIPE gives you another reason to take sudden breathing changes seriously. During immersion, you shift more blood toward your chest; cold water and hard exercise can increase the pressure in the blood vessels around your lungs. If fluid then enters your lung tissue and air spaces, you can struggle to get enough oxygen.

You can find an explanation of this mechanism and its warning signs in Divers Alert Network’s guidance on immersion pulmonary edema. You can also read a 2016 study in Circulation that investigated the abnormal pressure response during submerged exercise in people with a history of SIPE.

Your practical takeaway does not depend on diagnosing that pressure response: you should treat unexpected breathing difficulty in open water as a safety problem first.

Recognise the signs that should end your swim

You cannot reliably distinguish SIPE from asthma, a heart problem, aspiration, or another emergency while you tread water. Instead of trying to name the cause, watch for a change that does not fit your effort or your usual response to swimming.

• You feel much more breathless than your pace would normally justify.
• You develop a persistent cough during the swim.
• You feel chest tightness or notice wheezing or rattling breathing.
• You cough up frothy sputum, especially if you see pink colouring or blood.
• You struggle to breathe comfortably even after you stop pushing the pace.

You do not need every symptom, and you should not wait for pink froth before seeking help.

You might initially blame a tight wetsuit, a fast start, or nerves. Those explanations can feel especially convincing when you have trained well and want to finish. But if you experience new, disproportionate breathlessness alongside coughing or chest symptoms, you should end the swim rather than test whether you can settle into a rhythm.

Use an exit plan, not a self-rescue fitness test

If you develop these symptoms, stop your hard effort and signal for assistance immediately. Use your event’s safety signal, call to a nearby paddler or lifeguard, and accept flotation support. Keep your airway above water and prioritise an assisted exit.

You should not turn a breathing emergency into a race back to shore.

1. Get help in the water. Alert your buddy or safety crew rather than quietly dropping behind the group.
2. Leave the water with assistance. Avoid further exertion where possible.
3. Stay upright and keep warm once ashore. Loosen restrictive equipment without delaying medical help.
4. Call emergency services for severe or persistent breathing difficulty, chest pain, confusion, fainting, or pink or bloody sputum. Follow the dispatcher’s instructions.
5. Seek prompt medical assessment for suspected SIPE, even if you improve after exiting. Do not re-enter the water or continue into the bike and run.

You may feel better relatively quickly after leaving the water. That improvement does not prove that you only experienced anxiety, and it does not give you clearance to restart.

Change your next open-water briefing

You cannot guarantee prevention with one warm-up routine or one equipment choice. You can, however, make a breathing problem easier to recognise and a rescue easier to carry out.

Choose support before distance

You should favour supervised sessions or organised venues with clear rescue arrangements. Before entering, identify your exit points, understand how to call for help, and agree on a signal with your buddy. If you use a tow float, treat it as a visibility aid and possible temporary support, not a substitute for a life jacket or rescue cover.

Review your start, kit, and drinking habits

You should check that your wetsuit fits without excessive chest or neck restriction. Give yourself a controlled entry and start rather than launching straight into an all-out effort. Avoid deliberately overdrinking before the swim; more fluid does not automatically mean better preparation. None of these steps makes you immune to SIPE.

Flag your medical history

If you have high blood pressure, a heart condition, or a previous unexplained episode of breathlessness while swimming, discuss open-water exercise with your clinician. If you have experienced suspected or confirmed SIPE, seek medical evaluation before returning: you can experience another episode. Your review may need to address underlying cardiovascular problems, not just your swim technique.

Keep your watch out of the decision

You do not need a high heart-rate reading, a slow split, or an alarming training score to justify stopping. Your watch cannot rule out fluid in your lungs. You can apply the broader habit of reviewing what your devices actually tell you from A Race-Season Data Reset for Endurance Athletes, but your symptoms take priority during an acute water-safety decision.

Make one rule before your next swim

Before your next open-water session, tell your buddy or support crew: if you develop unusual breathlessness or persistent coughing, you will stop and ask for help. Check the exit route and rescue signal together.

You can reschedule a training session. You should never use the next buoy to test whether a breathing emergency will pass.