Concerns have been raised for a beluga whale after it was seen in France's river Seine - thousands of miles from the icy waters of the Arctic sea, where it typically lives.
It refused food and looked starved, according to a local official on Saturday.
The beluga is slowly swimming in a basis between two locks, approximately 50 miles from Paris.
Vets will check its health, and then a decision will be made on how best to intervene.
Rescuers, who are unaware that the 4-metre mammal is not eating as it lacks energy or is sick, have tried giving the creature live trout.
"It didn't seem very interested," Eure department official Isabelle Dorliat-Pouzet told reporters.
The whale has strayed far from its natural habitat, swimming 160 km up the Seine, past the port of Rouen and towards the
French capital.
Markings were beginning to appear on its skin, a possible sign of deteriorating health.
The all-white beluga normally live in Arctic and sub-Arctic oceans, although they are known to sometimes venture into more
southern waters and can survive for a short while in freshwater.
In May, a sick orca separated from its pod died of natural causes in the Seine after attempts to guide it back to sea
failed.
A month later, another whale, believed to be a Minke, was spotted in the Seine.
No decision had been taken on how to return the beluga to the ocean, Dorliat-Pouzet said.
One option was to try and lead it back to open water.
Another was to remove it from the river and transport it, though Dorliat-Pouzet said it was unclear whether the whale was strong
enough for such a perilous operation.
Vets will first to attempt to inject it with vitamins.
"Few people think it will return 160 km to the sea on its own," Dorliat-Pouzet added.
