The dolphin was discovered on a beach by holidaymakers on Friday

Marine conservationists worked throughout the night on Friday to save the five-foot mammal which was too weak to swim back out to sea.

Rescuers are unclear about the cause of death, although they think it could have had a worm infestation.

It was spotted by holidaymakers on a beach near Saundersfoot on Friday and they reported it to the coastguard.

It's unclear was killed it although it could be worm infestation which caused malnutrition Terry Leadbetter

Terry Leadbeater, from the Seal Sanctuary in Milford Haven, said the dolphin was rescued near Wiseman's Bridge, but died on Saturday morning.

"We managed to get it into a 10-metre pool in Milford Haven but, at about 1100 BST, it had convulsions and died.

"Mid and West Wales Fire Brigade was on the scene and administered oxygen to the dolphin, but it didn't work.

"It's unclear was killed it although it could be a worm infestation which caused malnutrition.

"The dolphin was not fully-grown and was about two to three years old."

Mr Leadbetter added: "We were called on Friday afternoon by the coastguard and when we arrived on the beach there were literally hundreds of holidaymakers round the dolphin - we couldn't move.

"We decided to move it to a 10m pool so we could assess its condition.

"We got a stretcher and carried it to a trailer and took it to the pool at Milford Haven Docks."

The mammal, which weighed about 60kilos, was a common dolphin, usually found about 10 miles out at sea.

"A vet had taken blood from the dolphin and we looked after it overnight in shifts because it couldn't really swim and we were afraid it would drown.