Rescuers pull up a net as they rescue a beluga whale stranded in the Seine river at Notre Dame de la-Garenne, northern France, on August 9, 2022. Photo: IC

An ailing beluga whale that strayed into France's River Seine has died during a last-ditch rescue attempt, experts having decided to put the animal down to prevent further suffering, local officials said Wednesday.

The fate of the animal has captured the hearts of people across the world since it was first spotted in the highly unusual habitat of the river that flows through Paris, far from its usual Arctic waters.

Rescuers had overnight winched the male out of the River Seine for transfer to a saltwater pen, in a delicate final effort to save the life of the ailing mammal, which was no longer eating.

"Despite an unprecedented rescue operation, we must announce with sadness that the cetacean has died," the authorities in the Normandy region of Calvados tweeted, adding that the whale had to be put down during transport.

After nearly six hours of work by dozens of divers and rescuers, the 800-kilogram ­cetacean was lifted from the ­river by a net and crane at around 4 am (02:00 GMT) and placed on a barge under the immediate care of a dozen veterinarians.

The beluga was then given a health check and driven in a refrigerated truck at a deliberately slow speed to the coastal town of Ouistreham to the north where experts decided to end its suffering.

"During the journey the vets noted a worsening of his health and in particular the breathing," said Florence Ollivet-­Courtois, a vet for the local emergency services, in a video posted on social media.

"The animal was not getting enough air and suffering ­visibly. We therefore decided that it made no sense to set it free and proceeded to euthanasia."

"The transfer was risky, but essential to give an otherwise doomed animal a chance," added the Sea Shepherd NGO, which has been assisting in the rescue, on Twitter.

"Following the deterioration of his condition, the vets took the decision to euthanize him. We are devastated by this tragic outcome that we knew was very likely," it said.

Upon arrival, the beluga was to have been installed in a seawater pen enclosed by a lock at Ouistreham pending release back into the wild.

"The beluga is a male who does not show any sign of infectious disease but who no longer has any digestive activity, which explains why he is no longer eating," said the Sea Shepherd NGO.

The four-meter whale was spotted more than a week ago heading toward Paris and was stranded about 130 kilometers inland from the Channel at Saint-Pierre-la-Garenne in Normandy.

Since Friday, the animal's movement inland had been blocked by a lock at Saint-Pierre-la-Garenne, 70 kilometers northwest of Paris, and its health deteriorated after it refused to eat.

While belugas migrate south in the autumn to feed as ice forms in their native Arctic ­waters, they rarely venture so far.