The body of a man aged in his early 20s has been recovered from the River Thames near Hampton Court.
He was reported to be in the water just before 4.15pm on Sunday and a major search was launched by officers from the Metropolitan and Surrey Police, London Fire Brigade and the RNLI.
At around 10.30pm a body was pulled from the water by police divers. The man's family have been told.
Metropolitan Superintendent Richard Smith said: "Our thoughts go out to the young man who has lost his life. Our officers worked incredibly hard with partner agencies but despite a rapid response he could not be rescued.
"We recently saw another tragic incident in which a young boy died after entering the Thames at Tagg's Island. I must again sadly reiterate the dangers the water poses.
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"It may look appealing but the danger and risk of loss of life is incredibly real. Please do not enter the water at any point. The consequences are enormous and we do not want to see any more families having to suffer such terrible news."
Since the unprecedented heatwave in July, more than a dozen people have drowned in British waterways as they tried to cool off.
The fatalities have prompted fresh warnings from fire services across the country, urging people not to enter unknown water despite the rising temperatures.
Surrey Fire and Rescue Service issued a stark warning after the body of a man was pulled from the River Thames on Friday, August 12.
A spokesperson said: "Do not jump into unknown water – it can be colder, shallower and faster flowing than it looks."
It comes as a teenage boy died off the coast of Skegness after a desperate five-hour search involving the coastguard helicopter which ended in the early hours of Monday morning.
Tragedy struck during what was another extremely busy weekend for emergency services stretched to breaking point by the heatwave that has blitzed much of the country.
Police said emergency services were called to a report that a child under 16 was in the water at about 6.15pm on Saturday (August 13), and, following a search by police, coastguard and lifeboats, the boy's body was found at around 11.30pm.
The identity of the teenager has not yet been released.
The tragedy came on a busy weekend for the popular seaside resort, with Superintendent Lee Pache of Lincolnshire Police, revealing that they received a high volume of calls for missing people, including 10 pleas for help in just two hours on Saturday.
