In the wake of the heatwave, the fire service is urging residents to stay safe around open water.
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Buckinghamshire Fire & Rescue Service has issued the reminder for anyone who will be near rivers, lakes or the coast.
The service warns that even on hot days, cold water shock can happen suddenly.
A spokesman for Buckinghamshire Fire & Rescue Service said: "Call 999 immediately and ask for the Fire Service. Encourage the person to float on their back. Throw rescue equipment if available. Never enter the water yourself to attempt a rescue."
Entering the water could put you at risk from cold water shock and strong currents.
The service recommends waiting for trained crews to arrive.
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