The beluga, extracted from the Seine in an overnight rescue operation, died on its way to Ouistreham in Calvados.
This was announced by the Prefecture of the department.
The beluga, discovered more than a week ago in the Seine, was euthanized during the transfer from a lock of the Eure to the port of Ouistreham, where it had to stay a few days to be treated.
"Despite an unprecedented rescue operation for the beluga, we are sad to announce the death of the cetacean," the prefecture announced on Twitter.
The animal was sick and could not feed.