Experts are looking at a plan to transport a malnourished beluga whale that has swum up France's River Seine back to sea before its health deteriorates any further, officials said Monday.

Sub-prefect Isabelle Dorliat-Pouzet of France's northern Eure department said they were seriously considering the option.

"In the interests of this beluga it can be attempted," she said. "We are working hard on it." 

But she was unable to say when they might make the attempt.

Officials in the prefecture of the Eure told AFP that the whale could be transported on a barge, overland or even by helicopter.

But the challenges are considerable, given they would be transporting a creature that weighs some 800 kilograms and is already sick and malnourished.

It would be a journey of 130 kilometers just to get to the north coast of France.

Members of environmental group Sea Shepherd monitoring the whale said Monday that it was no longer swimming upriver.

But it was still not eating, Sea Shepherd France President Lamya Essemlali told AFP in a text message. There was, however, "no worsening of its condition," she said.

The whale was first spotted in the ­river that runs through Paris to the Channel on August 2. 

Since Friday, it has been between two locks some 70 kilometers north of Paris.

The last-ditch bid to save the animal is partly because of fears that the river's warm water is harming its health.

Another alternative would be to open the locks in the hope that the beluga swims toward the Channel, authorities said.