Swimmers in Halkidiki, northern Greece, alerted the local coast guard on Wednesday after discovering a dead dolphin on a a beach near the village of Dionyisou.
According to initial estimates by representatives of the conservation group Arion, the mammal is most likely a rhinoceros dolphin though the cause of its death remained unclear.
"Dolphins come out to shore either because they are sick or because they are injured, so we should not try to force them back into deep water," Arion said.
"The best course of action is always to alert the coast guard and then the Arion organization," it added.
Since its foundation in 2002, the organization has recorded 450 cases of dead dolphins and whales being found on Greek beaches.