How warm or cold may the water be, and when are wetsuits worn?
A · Advanced · The competition · 3 of 4The water should be between 16 and 31 degrees Celsius, measured two hours before the start. Below 18 degrees wetsuits are compulsory. At 18 degrees and above they are not allowed, except that the chief referee may make them mandatory up to 20 degrees when conditions are hazardous.
How it works
- The range: "The water temperature should be a minimum of 16.0°C and a maximum of 31.0°C."
- How it is measured: on the day of the race, two hours before the start, at three points round the course at a depth of 40 cm. The agreed temperature is the average of the three.
- Who is present: a referee, a member of the organising committee and one coach chosen at the technical meeting.
- Below 18 degrees: "the use of wetsuits is compulsory".
- 18 degrees and above: wetsuits are not permitted.
- The exception: in hazardous conditions the chief referee, on the recommendation of the safety and medical officers, may declare wetsuits mandatory in temperatures up to 20.0 degrees.
- What a wetsuit covers: the torso, back and thighs completely. It may not extend beyond the neck, wrists and ankles.
- Swimsuits: at 18 degrees and above, a suit may not cover the neck, pass the shoulder or go below the ankle.
- Grease: competitors may use grease or similar substances, provided the chief referee does not think the amount excessive.
- During the race: the safety officer monitors the temperature.
Tricky cases
The water is 17 degrees. Can a swimmer choose to race without a wetsuit?
No. Below 18 degrees wetsuits are compulsory.
The water is 19 degrees and a swimmer feels the cold. Can they wear a wetsuit?
No, unless the chief referee has declared wetsuits mandatory for everyone because conditions are hazardous.
The water measures 31.5 degrees two hours before the start. Does the race go ahead?
It depends on the chief referee. The rule says the temperature "should be" no more than 31.0 degrees. The safety and medical officers advise on whether conditions are suitable.
Can swimmers cover themselves in grease against the cold?
Yes, as long as the chief referee does not consider it excessive.
Why the rule exists
Both ends of the range can kill. Cold water takes heat from the body faster than hard swimming can replace it, and warm water stops a swimmer shedding the heat they produce. A wetsuit also adds buoyancy and speed, so the rule makes it all or nothing: everyone wears one or nobody does.
Where it differs
| Where | What changes | Source |
|---|---|---|
| World Aquatics rules | As above | OWS 7.1 to 7.3; OWS 9.1.6.3; OWS 5.11 |
| Pool swimming | 25 to 28 degrees, and suits end at the knee | Swimming Rules 15.11.1; Part One, Article 7 |
| Triathlon | Its own temperature and wetsuit table | World Triathlon rules |
From the rule book
World Aquatics, Competition Regulations, Part Three: Open Water Swimming Rules (in force as from 1 January 2025), Articles 3.12.6, 5.11, 7.1 to 7.3 and 9.1.6. Checked 14 October 2026. Official document: World Aquatics Competition Regulations (PDF).