A stranded beluga whale in France's River Seine that has not been eating is now no longer progressing but is still "alive", according to environmental group Sea Shepherd.

Hopes are fading to save the animal, which was first spotted last Tuesday in the river that runs through Paris.

"It is alert but not eating," Sea Shepherd France president Lamya Essemlali told AFP news agency. There is "no worsening of its condition," she added.

Since Friday, the whale has been between two locks some 112 kilometers north of the French capital.

Rescuers are considering last-ditch efforts to extract the animal from the Seine, as the river's warm water is harming its health.

One alternative would be to open the locks in the hope that the beluga will swim towards the English Channel, authorities said.

But opening the locks would harbor the risk of the whale moving further upriver towards Paris, which would be even more disastrous.

Several attempts to feed the whale have failed in the past days. 

A three-person team from Marineland, Europe's biggest sea animal theme park located in the southern French resort of Antibes, is now arriving to help out.

"We've been following the operations at a distance from the start," said Isabelle Brasseur, in charge of education, research and conservation at Marineland.

"We are slowly making progress," she said. "There's not an ideal solution, we must weigh the pros and the cons" of each option to rescue the whale.

One of the experts on the team is a specialist for sea mammals, Brasseur said, adding they were bringing a stretcher and other equipment to try and move the animal.

On Saturday, veterinarians administered "vitamins and products to stimulate its appetite," said a statement from the police in Normandy's Eure department, which is overseeing the rescue effort.

Belugas are normally found only in cold Arctic waters, and while they migrate south in the autumn to feed as ice forms, they rarely venture so far. An adult can reach up to 13 feet in length.

According to France's Pelagis Observatory, specialised in sea mammals, the nearest beluga population is off the Svalbard archipelago, north of Norway, 3,000 kilometres from the Seine.