The couple, both aged 31, were found on Thursday in a moat surrounding the Vauban fort in the Chausey archipelago, off France's north-western coast.
The man was found early on Thursday morning in a dried out part of the moat.
His partner was found later in the afternoon in water that was 1.5 metres deep.
(The couple died off the north-west coast of France. Photo: GoogleMaps)
A local police officer was initially unable to give any clear indication of how the couple may have died, only saying that "the couple was found naked, with their belongings above".
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If indeed the couple fell - or jumped - from the fortress walls, they would have undertaken a ten-metre drop.
On Thursday evening, a police source told the Le Figaro newspaper that the death was accidental and likely occurred when the couple were "making love and something went wrong".