Officials in France are set to use orca sounds to guide a killer whale that strayed from the Atlantic Ocean and got lost upstream in the River Seine.

"The use of these non-invasive methods, from several hundred meters (feet) distance, will make it possible to avoid using ships in the immediate proximity of the animal, which could aggravate its stress and endanger its survival, as well as the safety of rescuers," the Seine-Maritime prefecture said on Twitter on Friday.

Local authorities plan to monitor the whale's location with a drone — while also emitting recordings of orca songs to coax it back to the sea.

The orca was first spotted by crew members of a trawler about 30 kilometers (18.6 miles) off the northern coast of France on April 5, Marine Mammal Research Group GEEC said.

The orca has since been sighted multiple times in the river, even about 60 kilometers upstream in the Seine near the small municipality of Yainville.

Worsening health

Experts have raised concerns that the marine mammal's health is deteriorating in the fresh water of the river.

Observers have seen signs of fungal infection and believe that the whale is emaciated.

A researcher tracking the whale told local media that it is now at risk of dying.

"It is in a life-threatening condition ... its state of health is very poor," Gerard Mauger, vice president of GECC, was quoted as saying on  the website of broadcaster France 3.

The 4-meter orca has been identified as a male.

In the past few weeks, several local media outlets have shown videos of the killer whale in the river, with its dorsal fin sticking out of the water and its unique black and white coloring showing as it comes to the surface for air.

dvv/rs (Reuters, dpa)