According to local folklore, Dozmary Pool is the spot where King Arthur returned Excalibur after being fatally wounded in the Battle of Camlann.
It is said to have been accepted by the Lady of the Lake, whose arm mysteriously rose from the water to received the fabled blade.
Now, some 2,000 years later, seven-year-old Matilda Jones stumbled across a 4ft long sword in the waters of Dozmary Pool during a family holiday.
She was paddling waist-deep on August 29 when she noticed the blade, which looks alarmingly like a medieval fighting weapon.
Ironically, her father Paul Jones, 51, had recounted the story of King Arthur to Matilda and her sister Lois, four, moments before the discovery.
Paul, of Doncaster, south Yorks., said: "It was a blistering hot day and Matilda asked if we could go for a paddle.
"She was only waist deep when she said she could see a sword.
"I told her not to be silly and it was probably a bit of fencing, but when I looked down I realised it was a sword. It was just there laying flat on the bottom of the lake.
"The sword is 4ft long - exactly Matilda's height."
Legend has it that King Arthur first received Excalibur from the Lady of Lake in Dozmary Pool after rowing out to receive it.
After being mortally wounded in the Battle of Camlann he asked to be taken there so he could return the sword to her.
After three attempts, his loyal follower Bedivere cast it into the water and the Lady of the Lake's arm rose to receive it.
The pool, in the civil parish of Altarnun on Bodmin Moor, was said to be bottomless until droughts in 1859 and 1976 dried it out completely and revealed it is, in fact, and shallow pond.
And Matilda's dad reckons the sword is probably only around 30 years old.
"I don't think it's particularly old," he said. "It's probably an old film prop."