Experts are not sure how they got there, and they’re worried about an explosion of the species, but anglers and swimmers have been told to be wary after large piranhas were found in one of the country’s most popular rivers.

Always use a disgorger……..

The South American piranha is a threat to tens of thousands of visitors who have been warned to be on their guard after the killer fish were caught by local anglers.

One expert said of the Amazonian fish: “I’m terrified of what could happen if the fish start to breed. There is a thermal spring nearby making the conditions perfect for it.”

Tens of thousands of visitors are drawn to the area each year because of the warm water as well as hundreds of anglers who hope to catch carp.

Fisherman Stefan Bielik, from Nove Mesto nad Vahom in the west of Slovakia, was amazed when he caught a piranha.

He said: “I was fishing for carp when I suddenly got a sharp tug on my line. When I reeled it in I found a 12 inch piranha dangling on the end.

“I’ve never actually seen one in real life, but I recognised it from its sharp teeth immediately.”

“It seemed really vicious and I would recommend people to stay out of the water. I managed to put it in my bucket and even though the lid was on it kept throwing itself against the glass trying to jump out.”