US tourists on a helicopter ride over western Iceland spotted about 50 dead pilot whales on a beach, radio station RUV reported.
The whales were discovered by the tourists on Thursday as they flew over the remote Snaefellsnes peninsula.
They took a video of their discovery and alerted police.
Despite their name, pilot whales belong to the dolphin family.
It is not clear why they washed ashore or how long they had been there.
Marine biologist Edda Elisabet Magnusdottir told the station that one explanation for the mass stranding could be that pilot whales are pack animals with strong social ties, which means that they would be likely to follow other pilot whales ashore.
In addition, she said there are strong currents in the area and the shallow seabed makes it harder for them to swim back into the open water.
Robert Arnar Stefansson of the Icelandic Institute of Natural History told RUV that while it is not uncommon for pilot whales to be stranded at this time of year, the number of whales stranding is unusual.