A 7.6-metre (25-foot) whale died on a beach in northern France on Monday, hours after being discovered washed up and alive but wounded, authorities said.
Experts had hoped the rising tide would come in time to help the cetacean back on its way, but the animal died as it struggled to reach the water.
"It probably drowned" during its efforts, said Jacky Karpouzopoulos, head of CMNF, an association for the protection of wild mammals in northern France.
The appearance of this type of beaked whale, a northern bottlenose, this far south is rare.
"These animals usually swim deep in Arctic waters," said Thierry Jauniaux, a sea mammal expert at Liege university in Belgium.
The female cetacean, weighing 3.5 tonnes, probably ended up on the beach "because it was disorientated", Karpouzopoulos told AFP.
"I've never seen anything like it in my 40 years on the job," he said.
Experts had ruled out lifting the animal back into the water, hoping that the tide would allow the animal to refloat and swim away, he said.
Jauniaux said a number of whales belonging to the same species have washed up recently on the coast of Belgium and the Netherlands.
This phenomenon could be due to "pollution, the appearance of new illnesses or increased sea traffic" leading to a change in the whales' behaviour, he said.
In February, a 9.5-metre female humpback whale was found dead on a northern French beach -- another "extraordinary" event, according to Karpouzopoulos.
In the spring of this year, an orca -- named "Sedna" by marine life protection group NGO Sea Shepherd -- was seen lost in the river Seine but died despite intense efforts to save it.
This summer, an ailing beluga whale that strayed into the Seine was put down by vets after a last-ditch rescue attempt failed because of its rapidly deteriorating health.