The dolphin-like whale was first spotted near the Athens coast on Thursday.
An ailing young whale found near the coast of Athens in a rare sighting has returned to deeper waters after receiving medication, Greek officials said on Saturday.
The male Cuvier's beaked whale is now swimming near the southern island of Salamis, deputy environment minister Georgios Amyras told state TV ERT, adding that its condition remained precarious.
The dolphin-like whale, which normally lives in waters more than 1,000 metres (3,280 feet) deep, was first spotted near the Athens coast on Thursday.
On Friday, wildlife experts and lifeguards were mobilised after it reached the shallows of a popular beach in the Athens suburb of Palio Faliro.
The whale was hydrated and given antibiotics and after several hours it was escorted to the open sea late on Friday, Amyras said.
"This is a deep sea animal...the longer it stays in shallow waters, the greater the damage to its health," he said.
Cuvier's beaked whales can dive up to 4,000 metres and usually grow to up to seven metres (23 feet) in length.
Natascha Komninou, a professor at the University of Thessaloniki and head of the Arion cetacean rescue centre, told Skai TV the whale had a badly wounded lower jaw and blood tests showed it suffered from anaemia.
"With such a major injury, things are difficult," she said.
Cuvier's beaked whales often fall prey to ship propellers, but they are also acutely sensitive to "noise pollution" from human activity, Komninou added.
Alexandros Frantzis, a marine biologist at the non-profit Pelagos Institute, this week said the whale could have become disoriented due to ongoing seismic research for hydrocarbons in the Gulf of Kyparissia in western Greece, one of the mammal's main habitats.
"It's one of the four most important habitats in the world for these animals."
"We are destroying their home...for hydrocarbons," Frantzis told ERT.
Although sightings of live whales are extremely unusual in Athens, whale carcasses occasionally wash up, mainly in the Greek islands.
A dead Cuvier's beaked whale was discovered on a small island near Crete in 2016, and another one was found on the island of Naxos the following year.
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