STORY: Rescuers overnight used a crane to lift the whale from the river. It was checked over by vets before being placed in a refrigerated truck for a road journey of more than 100 miles (160 km) to the channel port of Ouistreham.
"Despite an unprecedented rescue operation, it is with sadness that we announce the cetacean's death," said authorities in Calvados, the prefecture where the port is located.
A fire department vet said the beluga was euthanised while being transported after it developed breathing complications.
The plan was to move the whale to a saltwater basin in the hope it might recover some strength before being transferred to the sea.
The rescue attempt was risky for the beluga but marine conservation group Sea Shepherd France said the malnourished whale would not survive in the warm, freshwater river environment.
After its removal from the Seine, officials had warned of the animal's poor health.