Experts think the whale is sick and in a race against time for survival, she said.
The whale would remain in its temporary saltwater home for “two to three days” of surveillance and treatment before being towed out to sea, according to Isabelle Dorliat Pouzet, deputy prefect of the town of Evreux.
“Then, nature will take its course,” Pouzet said. “We have to be optimistic… the work has been painstakingly prepared.”
A team of some 80 people, including veterinarians and environmentalists, gathered Tuesday near a Seine River lock in the Eure region to plot the exodus of the new local celebrity.
Conservations groups said it would take 24 people to load the beluga into a refrigerated truck for the approximately 160-kilometer (99-mile) trip to Ouistreham, describing the the saltwater transfer as an “enormous operation.”
Because the region is experiencing extreme heat, the team plans to wait until nightfall before moving the ethereal white creature. It weighs about 800 kilograms (1,764 pounds).
Rescuers hope to spare the whale the fate of an orca that strayed into the Seine and died in May.
Authorities said that while the move carries its own mortality risk because of the stress on the animal, the whale can’t survive much longer in the Seine’s freshwater habitat.
They remain hopeful it will survive after it responded to a cocktail of antibiotics and vitamins administered in the last few days and rubbed itself on the lock’s wall to remove patches that had appeared on its back.
Sea Shepherd’s Essemlali said medical surveillance at the saltwater basin would help establish whether whale “is suffering from something we can help it with or from an incurable illness.”
Drone footage shot by French fire services last week showed the whale meandering into a stretch of the Seine between Paris and the Normandy city of Rouen that is far inland from the sea.
Conservationists have tried unsuccessfully since Friday to feed fish to the beluga. Sea Shepherd fears the whale is slowly starving in the waterway.