A killer whale that had become stranded in the river Seine and was due to be euthanized because of its "critical state of health" has been found dead.

Marine conservation group, Sea Shepherd France, confirmed on Twitter that "they have located the body of the orca that drew international attention after it was spotted swimming up the Seine River from Le Havre."

The group went on to say: "An autopsy will reveal the cause of death, but it was deemed too sick to rescue after one failed attempt."

Failed rescue attempt

Authorities launched an operation to save the stranded orca, but it ended in failure.

A group of experts recommended putting down the animal, French officials said on Sunday.

Local authorities said the animal appeared to be in a "critical state of health."

"The sound recordings also revealed vocal calls similar to cries of distress," said officials with the Seine maritime authority.

Scientists tried to lure it back to sea by playing orca calls. But the whale responded "erratically" and "incoherently" to the sounds emitted by a drone.

Officials believe that the whale was suffering from mucormycosis, also known as black fungus. The disease starts by spreading across the skin and can eventually reach organs like the lungs, the heart, and the brain, possibly explaining the animal's confused reaction.

A group of experts unanimously concluded that the only solution was to euthanize the whale and end its suffering.

Lone killer whale

The male 4-meter (13-feet) orca was first spotted in the French river on April 5 some 30 kilometers (18.6 miles) from the English Channel. It has since been spotted multiple times in the Seine, including around 60 kilometers upstream.

Killer whale sightings are rare in the English Channel. Some have speculated that the whale was there due to his illness, because relatively calmer waters made it easier to hunt.

Orcas can survive in fresh water but the environment is not good for their health. Additionally, orcas have a tight social structure and are used to hunting in packs, which poses additional problems for a stranded individual.

kb,dj/msh (AFP, Reuters, dpa)