A rare sighting of a Humpback Whale was made by the ORCA survey team on Thursday as the ship sailed near Dover en route from Southampton to Norway.
The team were alerted to the presence of a large whale by passengers who saw distinctive long pectoral fins slapping the surface of the water.
It is highly unusual to see one in the English Channel, so as a precaution the team have contacted the British Divers Marine Life Rescue in case the whale is lost, unwell or at risk of stranding.
A passing tug saw the mammal, a young female humpback measuring around 36ft (11 metres) long, off the Isle of Sheppey in Kent.
Local navigation warnings were issued to vessels in the area to be aware of the floating carcass before it was towed to Sheerness Docks, Thames Coastguard said.