Cold water shock

Cold water shock is the body's involuntary response to sudden immersion in cold water, typically described as an initial gasp reflex followed by rapid, uncontrolled breathing and a spike in heart rate and blood pressure. It happens in the first minute or so after unexpected immersion, well before hypothermia has time to set in, and it is a leading factor in drowning after a capsize, even for strong swimmers.

The danger of cold water shock is largely about timing and control rather than raw swimming ability: the involuntary gasp can pull water into the lungs if it happens underwater, and the rapid, panicked breathing that follows makes it hard to hold your breath, swim purposefully, or right a capsized kayak in the crucial first moments. Water considerably colder than the surrounding air temperature is enough to trigger it, which is why water temperature, not air temperature, should guide what a paddler wears.

Dressing for water temperature, using a wetsuit or drysuit layer in cold conditions, paddling with others, and staying close to shore in early season or cold-water conditions all reduce the risk this creates, but no single piece of gear removes it entirely. We recommend treating cold water as a real hazard whenever water temperature is meaningfully colder than the air, wearing a properly fitted PFD at all times, and getting instruction on cold water paddling before venturing into it; this entry explains the risk, it does not make any paddling activity safe.