Police investigating the disappearance of Bunmi Shagaya are preparing to lift an object from the swimming area of the lake near Dieppe.
There are unconfirmed reports a body had been found.
A senior police officer has frantically called for divers to search the spot where Bunmi was last seen alive.
Frogmen set out immediately on an inflatable launch before 13 police vehicles also rushed to the scene.
Officers in black overalls could be seen standing on the sandy shore while divers remained in the boat close to where police had been pointing. Waiting photographers and reporters were moved back from the scene.
It is four days since the 11-year-old from Lambeth, south London, went missing on her first school trip abroad.
Earlier classmates of the missing schoolgirl were reunited with their parents after returning from Cany-Barville in northern France.
Robert Blower, a spokesman for Lambeth Borough Council, in south London, said the returning teachers were "visibly shaken" as they handed the youngsters over to their waiting families at 5am.
Bunmi's relatives, her mother, two aunts and a cousin, have made an emotional visit to the scene of Bunmi's disappearance. Her father is planning to fly from Nigeria to London before making his way out to France.
The teachers from the school party are being allowed to rest today before Lambeth council officers begin asking their own questions.