Goldfish are categorized as an invasive species or pest in the wild by scientists, so their large populations are sometimes worrying. That's what happened in the city of Lethbridge, Alberta, Canada.
City officials are concerned about the growing population of goldfish and koi in some of the region's lakes. Apparently many people let their pet fish go there and cause problems.
This goldfish is able to survive in cold weather and has no natural enemies. So they can easily overtake the local fish population and disturb their habitat.
"They breed, win in competition with local fish and the population becomes very large," said Jackie Cardinals, natural resources officer in the town of Lethbridge .
"Another problem is that our lake is directly connected to the river, so if there is a flood, then there is a chance that this goldfish will go to the Oldman river," he added.
"This large population is caused by someone releasing these fish into the lake. They are not local fish, people put them there on purpose and created this very big problem," he continued.
Residents were also asked not to throw it carelessly and the authorities would try to suppress the fish population. In addition to disturbing local fish, goldfish can contribute to water quality degradation by ruffling sediments and uprooting plants.
On the one hand, goldfish are attractive as pets, but are considered bad for the environment if released. "All goldfish are basically invasive species all over the world. Across North America, Australia, parts of Europe, they're really widespread," said Przemek Bajer, an academic at the University of Minnesota.