We examined whether treatment for exertional heat stress via ice water immersion (IWI) or natural recovery is affected by the intensity of physical work performed and, thus, the time taken to reach hyperthermia. Nine adults (18–45 years; 17.9 ± 2.8 percent body fat; 57.0 ± 2.0 mL kg−1 min−1 peak oxygen uptake) completed four conditions incorporating either walking or jogging at 40 °C (20 % relative humidity) while wearing a non-permeable rain poncho. Upon reaching 39.5 °C rectal temperature (T re), participants recovered either via IWI in 2 °C water or via natural recovery (seated in a ~29 °C environment) until T re returned to 38 °C. Cooling rates were greater in the IWI [T re: 0.24 °C min−1; esophageal temperature (T es): 0.24 °C min−1] than the natural recovery (T re and T es: 0.03 °C min−1) conditions (p 0.05). Cooling rates for T re and T es were greater in the 39.0–38.5 °C (T re: 0.19 °C min−1; T es: 0.31 °C min−1) compared with the 39.5–39.0 °C (T re: 0.11 °C min−1; T es: 0.13 °C min−1) period across conditions (p 0.05), albeit occurred faster during IWI. Percent change in plasma volume at the end of natural recovery and IWI was 5.96 and 9.58 %, respectively (p
