Hypothermia is a potential risk for long distance swimmers (1). This case study describes a 39 year old female masters swimmer successfully completing an early season crossing of the English Channel from England to France (starting at 0333hrs 9th July 2019, ambient temperature 15.8 [1.0] °C cloudy and overcast during the day, water temperature 16.0 [0.1]°C, wind 5.5 – 15.0 kn SE direction, sea state slight). The swim was completed in 16 hours 1 minute, 2 days after a big spring tide, covering a total distance of 32 NM. Within this work, the thermal profile of the swim and lung function following the swim were documented. Informed consent to test and present these data were given. Whole body DEXA scans (Horizon, Hologic, US) were performed twice, 6 months and 7 days prior to the swim. Flow volume loops were measured at these time points and 2 days following the swim. The swimmer had no ill health during the 6 month training period and was sedentary for the 24 hours prior to the swim. Eight hours before the start, a gastro-intestinal (GI) temperature pill was ingested (e-Celsius, France) and temperature logged every 5 minutes for 52 hours. Tepid food and drink were given to the swimmer following pill ingestion. An increase in body mass of 16.4 kg occurred in the 6 months prior to the swim, the majority of that increased mass was fat (12.81 kg), with a small increase in lean mass (3.59 kg) and no change in skeletal mass (2.7 kg). In the hour before the swim, GI temperature increased from 37.1 °C to 38.5 °C at the point of entry into the water. GI temperature peaked (38.7°C) 40 mins after entry and cooled at a rate of 0.2°C.hr-1 for 11 hrs before stabilising at 36.5°C for the remainder of the swim. Recovery following the swim was unremarkable. Lung function was similar 6 months and 7 days prior to the swim (FVC; 6 months prior 4.25 L, 7 days prior 4.23 L, FEV1; 6 months prior 3.55 L, 7 days prior 3.65 L and FEV1/FVC; 6 months prior 83.53%, 7 days prior 86.29%), no complaints of breathing difficulties were made during or immediately post swim. However after 24 hours the swimmer complained of chronic wheezing and a tight chest, not improved with Salbutamol administration, reduced lung function was found 48 hours post swim (FVC; 3.74 L, FEV1; 2.52 L, FEV1/FVC; 67.11%). Symptoms were resolved with a 5 day course of oral steroids. Deep body temperature of Channel swimmers does not always reduce to levels considered hypothermic. Their tolerance likely results from their greater mass and fat percentage, having adequate fitness and fatness to generate and store heat as well as insulating against the cold. However, it is not clear why deep body temperature rose so quickly in the hour before the swim, the only explanation offered was nervousness. In addition, other factors affecting airway health need careful examination following long distance swims, even in those who are initially asymptomatic.