TEMPERATURES
OFFICIAL OPEN WATER TEMPERATURES
Temperatures as defined by various event and safety organisations/associations:
16°C. The lowest temperature for open water swimming events to reduce the risk of hypothermia (The World Aquatics - formerly FINA).
15°C & below. Defined as 'cold water' swimming (RNLI & other safety organisations).
That is, cold enough to pose a significant risk of cold shock (gasping, hyperventilation. increased heart rate/blood pressure, panic & impaired muscle control, potentially leading to water inhalation, heart attack or drowning). Swimmers are often required to complete a cold water safety induction, before being permitted to swim at organised OW sites.
5°C & below. Defined as 'ice Swimming' (International Ice Swimming Association).
GENERAL SWIMMER EXPERIENCE/PERCEPTION
Experienced open water swimmers often base their more nuanced scale on sensation, experience and acclimatisation, although water temperatures of 15° still remain a key safety marker.
25° & above. Often considered unsafe due to the risk of heat stress/heat exhaustion, as well as sun burn from the accompanying air temperature. Governing bodies often cancel races or ban wetsuits at this level.
24°-22°C. Commonly described as bath-like. Great for a casual swimming but too warm for serious performance training. Many marathon swimmers actively avoid these temperatures.
22°-20°C. Experienced swimmers in training often start to feel uncomfortably warm. Longer/harder sessions can become less productive, depending on the aim. For speed, this might be too warm; for distance/endurance (slower) perhaps less so.
20°-17°C. Generally considered comfortable.
16°-12°C. Often considered 'fresh' or 'nippy', which may trigger an involuntary gasp upon entry, although seasoned cold water swimmers often manage.
11°-6°C. Described verbally as 'freezing'. Swims are usually shorter and limbs tire/ weaken much quicker.
6°C & below. Considered 'baltic'. Generally only for very experienced individuals with appropriate experience, preparation and gear.
For ice swim/ice mile events, the maximum temperature permitted is 5° and 'gear' excludes wetsuits! 😱