Dead fish have been found clogging drains in the town of Telford in Shropshire County, England, causing a stinking problem for residents in the Madeley area.
The town has faced the issue of blocked sewages in the past when rubbish flushed in toilets caused such problems.
The latest incident was investigated after people complained of a fishy smell in their homes.
The authorities first thought it had been caused by owners flushing pet fish in the toilets but were shocked to find killer piranhas blocking the drains.
"We've certainly seen some weird things in the sewers over the years but we were a little shocked to remove piranhas," UK water company Severn Trent Water's workmen Matt Final and Jay Slater who investigated the smelly sewers said in a statement.
"You wouldn't think a fish of this size would fit down a toilet."
"It is just one example of amazing things we find blocking the sewers, but there is a serious aspect to this as they had the potential to cause a lot of damage."
Piranhas are flesh-eating fish found mostly in South American rivers. Telford residents were in a state of panic to learn about the presence of these dangerous creatures in the UK.
"If they've found some piranhas, it is surely feasible that there could be more still alive down there," Niall Poole, 22, from Madeley told Yahoo news.
Local butcher Jim Hoult, 56, added: "I might well be checking beneath the toilet seat before I go to the loo now."
However, the water company has now confirmed that the fish pulled out from the drain were not piranhas, BBC reported.
According to experts, the dead fish were more likely to be freshwater tilapia.