For years an elderly man has been terrorising captains on the idyllic Lake Starnberg - a hangout for the rich and famous in southern Bavaria.
“I am a big game hunter on the lake,” the man, who chose to remain anonymous, told Bild. “I love chasing the ships, and what a great feeling it is when they sound the horn!”
With flippers on his hands and feet, the impish oldie streaks stealthily through the water on his back, with only his mouth visible above the surface.
He then springs out of the water right next to the boat and forces the captain to swerve violently.
Unsuspecting passengers receive the shock of their lives when he emerges from the lake rather like the Loch Ness Monster.
One incredulous passenger exclaimed in Bild's video report: “He's got a screw loose!”
“It is completely dangerous,” a spokesperson for Starnberg Boat Trips - a company which provides tours around the lake - told The Local.
But the reckless pensioner is unperturbed by the risk of being turned to mincemeat by the propellers.
“With my flippers, I have such unbelievable strength that the propellers don't get me!” he told Bild
But irritated captains are forced to sound the horn, slam on the brakes and perform dangerous manoeuvres to dodge the mischievous septuagenarian.
“It's a very frustrating burden for the shipmasters,” said Ralph Schlemmert, operations manager of Starnberg Boat Trips.
The reasons for why the pensioner has taken up this strange habit remain something of a mystery. But one thing he told Bild hints at a form of revenge.
Twenty-five years ago, “a water safety boat accidentally rammed into my head whilst I was swimming [...] I was so angry,” he said.
For a long time, the police tried in vain to catch the devilish pensioner.
“Years ago they pulled me out of the water into their boat. But I just jumped out and swam away,” he claimed.
Whenever he was sighted, the boat company would call the cops and say, “The crackpot is back!” But by the time they arrived at the lake, it was too late.
But the game of cat and mouse could soon be over.
The police recently identified the man and are currently investigating the case, the spokesperson from the Starnberg Boat Trips told the Local.
This isn't the first time that people visiting Bavarian lakes have got more than they bargained for.
Earlier this month, an enormous two-metre-long catfish attacked a woman in a lake in south-eastern Bavaria. And last week a naked swimmer was hospitalised after a fishing hook pierced through his penis.