PARIS (Reuters) - The ailing killer whale adrift in the River Seine was found dead on Monday, campaign group Sea Shepherd said, after a plan to guide it back to sea failed and scientists concluded it was in agonising pain and terminally ill.

The 4-metre (13-foot) orca, identified as a male, was first spotted at the mouth of the Seine on May 16 between the port of Le Havre and the town of Honfleur in Normandy, before it swam dozens of miles upstream to reach west of the city of Rouen.

(Reporting by Juliette Jabkhiro, editing by Tassilo Hummel; Editing by Sudip Kar-Gupta)