A 40ft (12m) fin whale has tried to beach and is stuck against a pier wall in west Cork.
The creature came in to the harbour in Baltimore on a low tide and initially moved 328-437 yards (300m-400m) off shore before coming back to the small port.
The Irish Whale and Dolphin Group (IWDG) said from the description it is a young fin whale and maybe sick or starving.
Brendan Cottrell, assistant coxswain on the Baltimore lifeboat and owner of the Cape Clear ferry, said they were doing their best not to panic the creature further.
"We've been told to keep all the boats back and try not to stress the animal," he said. "It looks as though he's stuck by the pier wall and there's a crowd of about 200 or 300 looking on. We've had dead whales on the beaches before but never a live one in this spot."
Dr Simon Berrow, founder of the IWDG, said that from what he knows about the circumstances he is not confident the whale can be saved. "We've had this before on the south-west coast where whales have been emaciated and died," he said.
"It's hard to know. It's a young fin whale, it may be starving to death. If there is any chance of herding the whale out that is an option but it would need to be kept away from boat mooring lines in the harbour. But you want to keep back boats and people and jet skies, anything like that could stress the whale further."
Wildlife officers from the Department of Arts, Heritage and Gaeltacht Affairs have been notified.
Dr Berrow said the route the whale took into Baltimore, alongside Sherkin island, suggested that it would be difficult to herd the creature back out to sea.
It is understood some local boats had attempted to herd or encourage the whale out to sea early on Tuesday morning but the creature turned in towards the harbour.