The woman, thought to be in her sixties, was covered in cuts and bruises when she was spotted by a fisherman on the craggy outcrop on the isle of Krk.
Worried that his boat might run aground if he tried to rescue her himself, the fisher alerted police, who dispatched an emergency rescue team in two 4x4s. They had to abandon their vehicles and walk more than 3km to get to her.
Local officials told the website that the woman, who is 5ft 4in with shoulder-length brown hair and was wearing a pink sun hat, striped top and dark trousers, had no documents or phone that might have allowed her to be identified.
She was crying while sitting on rocks when found, according to Croatian newspaper 24sata.
According to The Evening Standard, a local resident told the newspaper: “It’s weird that she was looking in the area at all. It is an extremely inaccessible part of the bay with terribly sharp rocks, literally razors that cut the rubber on your shoes.
They added: “There is no life or animals except maybe wild boars or bears which know how to swim to here in search of food, but this is rare because there is no food, nothing.
“A woman that age certainly could not swim that distance, it needs exceptional strength.”
Police say it would have been impossible for a woman of her age and physical stature to swim the distance from a boat to the island.
The main question is how did the woman get there and who is she? Anyone who recognises the woman is asked to contact Ksk Police Station via primorsko-goranska@policija.hr.
She is being treated at a hospital in the Croatian mainland city of Rijeka.