Defining Cold Water
Why We Use 70F (21C) To Define Cold Water
Background
The temperature used to define cold water has important safety implications because it's the basis for recommending when paddlers and small watercraft operators should consider wearing thermal protection like wetsuits or drysuits.
In 1983, the US Coast Guard formally defined cold water as anything below 60F (15C), but as the result of a 1998 Congressional inquiry, they subsequently raised it to 70F (21C) - a much more sensible standard for boating safety.
The American Canoe Association (ACA) sets their thermal protection threshold at 60F (15C), and another paddling organization, American Whitewater (AW), recommends 50F (10C). Neither of these lower temperatures promote cold water safety.
Our Recommendation
The National Center for Cold Water Safety advises treating any water below 70F (21C) with caution. That's also the point at which we recommend thermal protection. We have scientific and practical reasons for this, both of which reflect a cautious and informed approach to Risk Management.
First, we know from scientific research that breathing control begins to be affected at water temperatures below 77F (25C). That's why the International Olympic Committee requires holding pool temperatures for competition between 77F – 82F (25C – 27.7C). Our 70F (21C) recommendation for outdoor safety is seven degrees below that point.
It's also consistent with boating fatality statistics like the ones in the 2024 Table below. They show that you're twice as likely to die in a boating incident in water below 70°F (21°C), and three times as likely to die when it's between 50-60F (10-15.5C)
Second, scientific research demonstrates that if you aren't physically acclimated to cold water, life-threatening cold shock symptoms reach maximum intensity between 50F-60F (10-15C). That means a complete loss of breathing control which can lead to sudden drowning.
Since very few people are acclimated to cold water, we feel that it's prudent to set the guidelines for thermal protection at a point that's well above the maximum-intensity cold shock range.
To people who are unfamiliar with cold water, 70F (21C) doesn't sound very cold because they mentally compare it to 70F (21C) air. But water is much denser than air, so it feels much colder, and it steals body heat 25 times faster than air.
Average skin temperature is 91F (33C). That's why 85F (29C) water feels cool and 70F (21C) water feels cold. When you get down to 45F (7C), the water is so cold that it feels like it’s burning your skin.
References:
An excellent publication with 176 references is Survival In Cold Waters (2003 / 2007), which was authored by Dr. Chris Brooks and published by Transport Canada. On pp16, in the section on cold shock, Dr. Brooks notes the following with respect to water temperature:
“...it is now known that the cold shock response begins at water temperatures below 25ºC (Reference 90) and peak at a temperature between 10-15ºC (References 154 and 155)”.
90. Keatinge, W.R. and Nadel, J.A. Immediate Respiratory Response to Sudden Cooling of the Skin. J. Appl. Physiol. 20:65-69, 1965.
154. Tipton, M.J., Stubbs, D.A, Elliott, D.H. Human Initial Responses to Immersion in Cold Water at Three Temperatures and after Hyperventilation. J. Appl. Physiol. 70(1):317-322, 1991.
155. Tipton, M.J. The Relationship Between Maximum Breath Hold Time in Air and the Ventilating Responses to Immersion in Cold Water. Eur. J. Appl. Physiol. 1992: 64: 426 – 429.