© Bruce FraserThe Hector's dolphin was found dead at the head of Milford Sound in Fiordland.
The Department of Conservation (DOC) said there were no obvious signs of the cause of death and the animal had been sent away to be examined.
DOC said while other dolphin species were seen in the sound, sightings of Hector's, either dead or alive, were rare.
It said while they inhabited the West Coast, they didn't usually travel this far south.
Hector's were nationally endangered with a population of around 10,000.
Comment: Also within the past few days a dead whale washed up on the coast of California while another appeared at a beach on Rhode Island.