NUDE swimming in Sweden has become risky business after an invasive species of fish infamous for attacking testicles was discovered in local waters.
Denmark's Natural History Museum has issued the warning after the eight-inch (21cm) fish - a relative of the pirana - was caught in an eel trap in Oresund Sound off the south coast of Sweden.
Known as a pacu, the "ball-cutter" fish has a set of chompers remarkably similar to human teeth.
Natural History Museum of Denmark fish expert Henrick Carl told Swedish news site The Local that the freshwater fish bite "because they're hungry, and testicles sit nicely in their mouth."
"It normally eats nuts, fruit, and small fish, but human testicles are just a natural target. It's not normal to get your testicles bitten off, of course, but it can happen ...," Mr Carl said.
The Natural History Museum kept its warning raw: "Keep your swimwear on if you're bathing in the Sound these days - maybe there are more out there!"
The pacu is normally found in the warmer waters of the Amazon. They can grow up to 90cm (35 inches) and 25kg.
The museum is testing the DNA of the fish to confirm that it is a pacu.
"They are almost identical to the piranha," Mr Carl told The Local. "It's just that they have different teeth. Flatter and stronger, perfect for crushing