Eyewitness Jackie Jones, 60, was on Kamari beach when she spotted a shade that she later identified as a shark. At one point, she explained, it started to dramatically circle the water with its fin out. She said the predator was just 50th from the shore.
Ms Jones and her husband Nev, from Cannock, Staffordshire, travelled to the Mediterranean island to celebrate his 60th birthday.
The secretary, a grandmother of two, said: “We’ve been coming to Kos for 20 years and we’ve never seen anything like it.
“I had only just got out of the water and I’m glad I did – I didn’t want to be its next meal.
“It was clearly feeding because it was on the surface and you could see his fin and his tail flipping around.
“We could see it swimming up and down doing a figure of eight coming back on itself and its tail was flicking across the water- we could see how big it was.
“I had a horrible vision that at any moment someone in the water would vanish like a real-life Jaws.”
Speaking to the Sun, the woman said the incident left her constantly checking if the shark was at the bay.
Although she struggled to feel safe at the beach the next day, she said she and her partner will return to their favourite holiday spot.
She said: We will definitely go back to the island. It hasn’t put us off going at all.”
The incident came as a shark bite in Cornwall left Britons adamant to swim in UK waters after a woman was left requiring hospital treatment.
Shark attacks in UK seas are rare yet not inexistent.
Blue sharks are an open-ocean species that is known to visit in the summer months and is usually spotted more than 10 miles offshore.
The largest blue shark ever caught in the UK weighed 256lbs (116kg) and measured over 9ft (2.74m).
On Thursday, a swimmer who was not named got bitten while snorkelling with sharks on an organised trip.
Despite being left with a leg injury, the woman said the creatures were “majestic” and hoped what happened to her would not “tarnish the reputation of an already persecuted species”.
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This is believed to be the first report of an injury caused by a shark attach since 2018.
Boat operator Blue Shark Snorkel Trips said in a statement that such occurrences are “extremely rare and can be easily misunderstood”.
They added: “The last thing we want is to let speculation drive the media into a world of bad press for the sharks, under no fault of their own.
“We immediately enacted our emergency response plan, with first aid being carried out on the person involved.
“Following advice and assessment from the coastguard, the person walked off the boat and received further treatment ashore.”
Last month, five beaches were shut after three sharks were spotted off the coast of a Spanish holiday hotspot.
Swimmers were banned from going in the water at beaches in Sitges and Vilanova i la Geltrú, near Barcelona.
Days earlier, the world’s fastest shark, which can reach speeds of up to 43mph, was sighted lurking off the nearby coast of Garraf.
Divers spotted the great mako shark, which can grow up to 15ft long, for the first time in 10 years.