Open-water swimming in cold and warm water: little evidence underpins water-temperature limits, acclimatised swimmers cannot judge their own thermal state, and cardiac events
Not only thermal responses — appear to be the primary cause of death; the review gives event-organisation guidelines
Key Findings
Open-water swimming (wild or competitive, including triathlon) is fast-growing, yet little evidence exists on which to base high and low water-temperature limits.
Acclimatisation dissociates thermal sensation and comfort from actual thermal state, so individuals cannot be left to monitor their own physical condition during swims.
Deaths have occurred during open-water swimming, from thermal responses and also cardiac problems; cardiac events appear to be the primary cause of death in open-water events.
The paper presents guidelines for organising open-water events to minimise risk and calls for more data on responses to cold and warm immersion, individual variation, and the precursors of cardiac events.
Practical Application
The leading cold-water group's review of open-water swimming concludes that water-temperature limits rest on little evidence, that an acclimatised swimmer's sense of comfort does not track their real thermal state, and that cardiac events appear to be the main cause of death — so treat cold and warm open water as a safety problem managed by organisers and companions, not by how the swimmer feels.
Never rely on "I feel fine" in cold or very warm water; swim with external monitoring (safety cover, companions) and respect event temperature rules even when they feel conservative.
Not from this paper; the base's own practice: build cold exposure gradually, control the first minutes after cold entry, insulate (wetsuit where permitted) in cold water, and pace and cool conservatively in warm water. Any chest pain, palpitations or breathlessness out of proportion in the water is a medical matter, not a performance one.
Limitations
Narrative review; the abstract itself states the evidence for temperature limits is thin. Individual thermal responses vary widely with body composition, habituation and water temperature.
The specific guideline values are in the full text and are not reproduced here.
How this entry was checked and changed
Why this level
regraded 2026-09-27 from B: authoritative narrative review from the leading cold-water immersion group (Tipton), no systematic method
Content correction 2026-09-27
Entry framed the paper as "performance and safety hinge on thermoregulation ... managed by acclimatization, pacing and insulation" -> the abstract's points are: little evidence for temperature limits; acclimatisation makes self-monitoring unreliable; deaths from thermal AND cardiac causes with cardiac events the apparent primary cause; organiser guidelines. The pacing/insulation/cold-shock-window advice was not in the abstract and is now labelled as the base's own practice.
Added the cardiac-death finding and the "cannot self-monitor once acclimatised" finding. Level regraded B -> B+ (authoritative narrative review, leading group); Tier set to 1-4 from "mixed"; Sport adds triathlon (abstract names triathlon).