Scientists issue an urgent warning about outdoor swimming during the current UK heatwave, cautioning that even relatively cold water can create serious risks for swimmers. The reports highlight that sudden exposure to colder water can trigger a “cold water shock” response, which can affect breathing and overall body function. Organisers and public health messaging emphasise that people may underestimate how quickly their body reacts when entering water that feels safe or refreshing after hot weather. The warnings also point to the potential for complications that can lead to distress in the water, particularly for inexperienced swimmers or those who enter without preparation. The guidance focuses on awareness of water temperature differences, including how quickly conditions can change between air and water during high temperatures. Overall, the outlets present the message that swimming during hot weather can still be hazardous if swimmers do not take appropriate precautions, as the immediate impact of cold water shock can be life-threatening in some cases.