The large animal, confirmed to be a minke whale, was discovered on Portstewart Strand on Sunday evening.
A makeshift cordon has been erected around the carcass, which is just metres from the main entrance to the beach.
On Monday, members of the public were pictured milling around the cordon, some taking selfies with the dead animal in the background.
A minke whale has beached and died at Portstewart Strand in Co. Derry. The Department of Agriculture, Environment and Rural Affairs (DAERA) said it happened on Sunday evening.
Photo by Jonathan Porter/Press Eye
The Department of Agriculture, Environment and Rural Affairs (DAERA) said the carcass was “likely” to be removed as soon as possible.
“On the evening of May 25 2025, a dead minke whale beached at Portstewart Strand was reported to DAERA,” they said.
“The cause of death is not known, but it is not uncommon for these marine mammals to die of natural causes and to be washed ashore.
“The National Trust, as the landowner for Portstewart Strand, is responsible for dealing with the carcass and has erected signage to ensure the public keeps clear of the situation.
“The National Trust is in contact with DAERA officials in determining the next steps. This is to ensure that both the public and sensitive habitats are considered in any action agreed.
“Given the location, which is so close to public access points to the beach, it is likely that the National Trust will seek to remove the minke whale from the site as soon as possible.”
A minke whale has beached and died at Portstewart Strand in Co. Derry.
Photo by Jonathan Porter/Press Eye
The National Trust said it was working with a “range of agencies and marine mammal experts to determine next steps” and has urged the public to keep a safe distance.
“Until this process is safely complete, we urge the public to continue to follow all signage and keep a safe distance,” said a spokesperson.
“Please also continue to keep dogs on leads and under tight control. Decaying marine mammals pose a serious health risk.
“They can carry a range of diseases that are transmissible to humans and dogs. Thank you for your understanding and support.”
Minke whales are one of the smallest species of baleen whale, growing up to around 33 feet in length.
They are regularly seen off the Northern Ireland coastline.
Laurence Ghisoiu, senior visitor experience officer for the National Trust, told BBC News NI that the organisation was working to ensure the whale was disposed of as quickly as possible.
Images from the National Trust
“It is sad but it is nature,” he said.
“Our main concern at the moment is the safety of our visitors so it is very important to keep away from it.”
The last whale to wash up on the shore at Portstewart Strand was a 30ft juvenile fin whale in 2015.
Back then, it was taken to landfill.
Prior to that a 31ft, seven tonne minke whale appeared on the beach in 1993.
It beached during a low tide and despite the efforts of many who battled for four hours to refloat the mammal, it died.
Minke whales can usually be seen in Northern Ireland between July and October in UK waters and live for up to 50 years.
Whales can come ashore for many reasons, including injury, illness, bad weather and navigational errors leading them into shallow water.
Emergency services have been contacted for comment.