At least three people have died in France due to suspected cardiac arrest after jumping into water.
The swimmers are thought to have died of “hydrocution”, that is any poorly-diagnosed, sudden death that takes place in water, but is not due to drowning but because of temperature differences.
Europe has been put on high alert as a deadly heatwave is sweeping through the continent.
Temperatures are due to surpass 40 degrees Celsius in several parts of the continent.
A man aged 70 died after jumping into cool water at Marseillant beach, southern France, a woman aged 62, died at Frontignan beach near Montpellier after “having a malaise and drowning” and a man aged 75 also died at another beach nearby.
Firemen in France have warned people to enter the water gradually to accustom the body to temperature changes or risk hydrocution.
As reported earlier, forecasters have warned of a deadly heatwave that will pose a threat to lives with France expected to experience the hottest June on record.
Public warnings have since been issued in France, Spain and Germany amid fear of losing many lives.
The European forecasters say the heatwave has brought sad memories of the continent’s 2003 heatwave which saw 15,000 people perish as temperatures reached a peak of 111F (44.1C) in mid-August.
Temperatures are climbing to 104F (40C) and above in some cities.