-7°
At this temperature, salt water with a 10% concentration (10 g of salt per liter) freezes.
-2°
This is when seawater starts to freeze (for the least salty seas).
0°
Fresh water freezes and turns into ice.
A person who falls into 0°C water cannot survive more than 30 minutes.
4°
This is the temperature of Lake Baikal, where Stève Stievenart (also known as Stève the Seal) swam 55 kilometers in 21 hours without a wetsuit — after extreme preparation that included gaining 47 kg of fat and eating like a seal: five meals of fish per day.
5°
Below this temperature, an untrained person who falls into the water will not survive more than 45 minutes.
It’s also the maximum temperature allowed for an official ice swimming competition.
10°
The maximum temperature allowed for an official cold-water swimming competition.
At 10°C, an unprepared swimmer’s survival time doesn’t exceed 2 hours.
Note: For both ice and cold-water disciplines, the temperature is measured between 10 and 30 cm below the surface at three different points along the course or pool. The three thermometers must show values within 1°C of each other.
14°
Exceptionally, this is the lowest temperature authorized for an open-water event.
15°
At this temperature, a person’s survival time does not exceed 6 hours.
16°
This is the minimum temperature (without exemption) for an official open-water swimming competition.
Below this temperature, wearing a wetsuit is mandatory in triathlon.
18°
Since 2023, this is the temperature below which a neoprene wetsuit and cap are mandatory for open-water events governed by the French Swimming Federation (FFN).
20°
From this temperature upward, neoprene wetsuits are no longer allowed in official events under the FFN or the French Triathlon Federation.
26°
The recommended water temperature by U.S. Masters Swimming, equivalent to 80°F (26.6°C) for official competitions.
27°
The water temperature used in the Paris 2024Olympic pools. World Aquatics (FINA) recommends this temperature (±1°C) for official competitions to keep athletes in optimal conditions.
Note: Water that’s too cold can cause shock, stiffness, and difficulties with breathing and movement. Water that’s too warm can lead to overheating, forcing swimmers to slow down or stop to protect their body.
31°
The maximum authorized temperature for open-water and triathlon events. Beyond this, the risk of hyperthermia becomes too high.
32°
Generally considered comfortable for being in still water (without movement) without feeling cold. Of course, this depends on the individual’s body type, health, fatigue level, and weather conditions.
38–40°
The maximum temperature for spas and hot tubs, slightly above normal body temperature.