From pool to open water: why you feel out of air even with a good CSS
Many triathletes swim well in the pool, then feel panicky or short of breath in a lake or the sea. CSS describes your pool speed, not how you will feel in open water. This guide explains common reasons and a progressive, safety-first way to prepare. It is general information, not medical advice.
Open the Critical Swim Speed CalculatorWhat CSS does and does not tell you
Critical Swim Speed is a pool pace based on a 200 m and a 400 m test. It measures speed in a controlled setting with walls, lane lines and a clear bottom. It does not include cold water, waves, other swimmers, a wetsuit or the sensation of having no wall to hold. A good CSS means you have the fitness, not that open water will feel easy.
Why open water feels different
- No walls and no black line. Without constant reference points, many people feel exposed and swim tense.
- Cold water can make you breathe faster at first. Gradual entry and a warm-up in the water help.
- A wetsuit can feel tight around the chest and neck, especially if it is new or does not fit well.
- Sighting, waves and other swimmers interrupt your rhythm and your breathing pattern.
- Anxiety itself speeds up breathing and makes it feel shallow, which can then feel like you are out of air.
These are common experiences, not a diagnosis. If you ever have chest pain, dizziness, severe or unusual breathlessness or symptoms that continue after you get out of the water, stop, get out safely and speak to a doctor before swimming again.
Safety first
- Do not swim alone in open water. Use a supervised venue, a club session or a buddy who stays with you.
- Use a brightly coloured cap and a tow float so others can see you and you have something to rest on.
- Check the water temperature, weather, currents and local rules before you go, and stay close to the shore at first.
- Know how to ask for help: raise an arm, float on your back and signal.
- If you feel panic building, stop swimming, roll onto your back or hold your float, breathe slowly and wait until you are calm before you continue.
A progressive build-up
| Step | What to do | Aim |
|---|---|---|
| 1 | Swim longer continuous sets in the pool with fewer rests at the wall | Get used to continuous swimming |
| 2 | Swim in your wetsuit in the pool or in shallow water | Get used to the feel and the fit |
| 3 | Enter open water at a supervised venue and float and breathe for a few minutes | Settle your breathing before swimming |
| 4 | Swim short sections near the shore, stopping whenever you want | Build confidence without pressure |
| 5 | Add sighting every few strokes and swim in a straight line | Learn to navigate |
| 6 | Practise with other swimmers and a race-style start at the edge of the group | Get ready for race conditions |
Stay at each step until it feels manageable. There is no benefit in rushing, and returning to an earlier step is normal.
Pace and breathing in open water
- Start well below your pool CSS pace. Effort matters more than speed in open water.
- Breathe out steadily into the water, and avoid holding your breath between strokes.
- If your breathing gets short, slow down, roll onto your back or switch briefly to breaststroke to reset.
- Do not use your CSS to predict your open-water pace exactly. Measure it on the day and in the same conditions you will race in.
On race day
- Warm up in the water if the race allows it, and get your breathing settled before the start.
- Start at the side or at the back of your group, away from the busiest line.
- Know the race rules on stopping, holding a buoy or kayak and asking for help. Rules vary between events.
- If you need help, raise an arm and call, and stay where you are until a safety crew reaches you.
FAQ
Why do I feel short of breath in open water but not in the pool?
Common reasons include cold water, a tight wetsuit, the lack of walls and anxiety, which all affect breathing. This is general information. If the problem is severe or unusual, speak to a doctor.
Does a good CSS mean I am ready for open water?
No. CSS describes your pool fitness. Open-water comfort is a separate skill that needs practice in safe conditions.
Should I swim alone to practise?
No. Swim at a supervised venue or with a buddy and use a tow float.
Can I use CSS to set my open-water pace?
Use it as a reference only. Start below it and measure your own open-water pace in training.