Two piranhas are being tested after their dead bodies were discovered in a Yorkshire lake.
It is currently a mystery as to how the fish, usually native to South American rivers, were found in Martinwell Lake in Edlington Village.
The popular walking and fishing spot is owned by Doncaster Council and a spokesman for the authority said the dead fish have been taken for examination.
Assistant director of environment at Doncaster Council, Gill Gillies, said it was likely that the fish were unwanted pets.
"Given the natural habitat of piranhas, it is highly unlikely that the fish were alive at any time in the lake," she said.
"We assume that these were pets that were placed in the lake, something that we would strongly discourage people from doing."
Villagers of Edlington had speculated that the fish could be responsible for the decline in the number of ducks living on the lake.
However, experts have said it would be virtually impossible for the fish to survive in Yorkshire-temperature waters.
An Environment Agency spokesman said: "Piranhas are not native to England and do not belong in our rivers and lakes.
"These fish do not easily survive or feed at temperatures below 10C and readily succumb to the cold of northern winters.
"We would encourage anyone that keeps exotic fish and which may have outgrown their tanks, to contact a specialist able to advise on how best to deal with them."
He reminded people it is illegal to release or transfer fish in England without an appropriate permit as well as keeping non-native species in the wild without a permit.
Words by Wesley Hudson.