Skinny-dipping in Sweden and Denmark is ill-advised this summer after fisherman there spotted the vicious pacu fish, a native to the Amazon, in their nets.

An eight-inch pacu was caught in the Oresund Sound between Sweden and Denmark.

The freshwater fish is said to have a proclivity for attacking men's testicles while they swim or fish, earning it the nickname "ball cutter."

"Keep your swimwear on if you're bathing in the Sound these days — maybe there are more out there!" the Danish National History Museum warned those who enjoy bathing au naturel.

More from GlobalPost: Pacu, the testicle-eating fish, found in Illinois lake

Apparently the omnivorous fish has taken the testicles of many a fisherman along the Amazon, some of whom fatally bled out in rural, isolated locations. They have also munched the manhood of fishermen in Papua New Guinea — odd for fish considered the friendlier, vegetarian version of the piranha.

In July 2012, the ball cutters, which can weigh up to 55 pounds, were found in Lake Lou Yaeger in Illinois.

Though Swedish fisherman seem to have been unscathed, more pacu may be lurking, and likely wondering why the water's so much colder than they're used to.

From Illinois to Denmark, the fish were most probably dumped by exotic pet collectors —an illegal act, no doubt, and one that strikes fear in the hearts of fisherman and swimmers the world over.