A city in the US state of Minnesota has urged residents not to release their unwanted pet fish into the wild after finding huge goldfish in a lake.
The common household pets can grow far bigger in the wild and cause major disruption to ecosystems.
The city of Burnsville shared images showing several monster goldfish caught during a survey of Keller Lake.
It said goldfish could contribute to poor water quality by disturbing sediment and uprooting plants.
“Please don’t release your pet goldfish into ponds and lakes!” the city wrote in a tweet.
In Minnesota, goldfish are a regulated invasive species, which means it is illegal to release them into public waters.
A goldfish kept in a home aquarium typically grows to about 2in (5.1cm) in length.
But once they are established in public waters, wildlife officials say, goldfish can grow far larger and be difficult to remove – reproducing rapidly and dominating native species.
In its warning, the city of Burnsville advised pet owners to “please consider other options for finding them a new home”.
Wildlife officials have been dealing with a similar problem in nearby Carver County, where 50,000 goldfish were removed from a creek in October last year.
The removal was part of a three-year plan to study and manage the species, which have caused problems across the US.
But the US isn’t the only country to suffer from marauding goldfish.
In 2017, Munich city council in Germany said shoals of goldfish were starving out all rivals in local ponds and lakes. The problem got so bad, the council threatened to fine anyone caught releasing their pets into public waters.
Large goldfish have been found in the UK’s wild waters as well. In 2010, a British teenager pulled a 5lb (2.2kg), 16in fish from a lake in Dorset.