A 4-metre-long orca that roamed the French river Seine since May 16 will be euthanased after multiple attempts to guide it back to sea failed.
The young whale, identified as male, swam upstream towards the city of Rouen after it was first spotted at the mouth of the river between the port at Le Havre and the town of Honfleur.
So far, the weakened animal has not been able to swim back to the ocean on its own strength.
After a failed rescue attempt with a drone that imitated orca sounds, to which the whale responded "erratically" and "incoherently", scientists concluded that the whale was suffering from a fungal disease.
Black fungus, a disease so far only observed in whales in North America, can spread to the heart, lungs and brain, explaining the animal's erratic behaviour.
The disease, which is in an advanced state and terminal for the orca, could contaminate other sea mammals.
French authorities are currently preparing to euthanase the whale.
