Football-sized goldfish have authorities in one Minnesota community urging residents not to release in local waterways.

Officials in Burnsville, Minnesota, captured nearly 30 gigantic goldfish, some measuring more than 18 inches and weighing up to 4 pounds, the Associated Press reports. The fish are believed to have been released by owners thinking it was a humane way to dispose of the unwanted pets.

City employees fished out the large lunkers from Keller Lake. The invasive species, a cousin of the common carp, can grow to prodigious sizes when allowed to swim free in open water, making it difficult for native fish to survive.

“Most of them were definitely bigger than you’d find in your typical aquarium,” Daryl Jacobson, the city’s natural resources manager, tells Erin Adler of the Minneapolis Star Tribune.

Burnsville officials took the unusual step of using social media to ask residents not to release gold fish in the wild, reports Ewan Palmer of Newsweek.

“Please don’t release your pet goldfish into ponds and lakes!” the city’s Twitter account states. “They grow bigger than you think and contribute to poor water quality by mucking up the bottom sediments and uprooting plants.”

Please don't release your pet goldfish into ponds and lakes! They grow bigger than you think and contribute to poor water quality by mucking up the bottom sediments and uprooting plants.Groups of these large goldfish were recently found in Keller Lake.

— City of Burnsville (@BurnsvilleMN) July 9, 2021

Goldfish swimming amok are a pervasive problem in many states and Canada, as well as Europe and Australia. The hardy fish survive well in low-oxygen environments and easily tolerate extremely cold conditions.

Nearly 30 Football-Sized Goldfish Caught in Minnesota Lake

Last November, more than 50,000 goldfish were netted at Big Woods Lake in Carver County, Minnesota, not far from Burnsville. Officials there are trying to restore the waterway, but they are wary the problem won’t go away.

“We don’t want to put all these resources in and remove these fish and get the lake back to a stable system, and then just have this happen all over again,” Andrew Dickhart of the Carver County Water Management Organization tells Kirsti Marohn of Minnesota Public Radio.

40-50 MILLION! That’s how many goldfish researchers believe are in Lake Ontario. @FishOceansCAN says they are also now in most lakes, rivers and water reservoirs across the country. Most from people dumping or flushing their pets.Tonight on @CTVNationalNews

— Peter Akman (@PeterAkman) September 14, 2018

Goldfish can cause poor water quality conditions in ponds and lakes by stirring up sediment and uprooting plants. According to the Carver County website, the one-time pets “reproduce rapidly and are hardy... They can live to be 25 years old, and once established, no easy solution exists to remove an invasive species like goldfish.”

Canadian authorities estimate that as many as 50 million goldfish may inhabit Lake Ontario. The population has exploded in recent years, which has impacted other species, Tys Theysmeyer of the Royal Botanical Gardens in Hamilton, Ontario, tells Peter Akman of CTV News.

“Populations of frogs, fish, turtles, salamanders—they’re all significantly down,” he says.

So, what should you do with little Goldie when you no longer want to care for them? The United States Fish and Wildlife Service recommends putting the fish up for adoption, donating it to a school or humanely euthanizing it with a veterinarian or pet stores’ assistance.

Whatever you do, don’t release it in a pond or lake—and don’t flush it down the toilet. In 2019, Smithsonian’s Meilan Solly reported how a 14-inch goldfish was caught downstream from a wastewater treatment plant on the Niagara River near Buffalo, New York.

David Kindy| | READ MORE

David Kindy is a daily correspondent for Smithsonian. He is also a journalist, freelance writer and book reviewer who lives in Plymouth, Massachusetts. He writes about history, culture and other topics for Air & Space, Military History, World War II, Vietnam, Aviation History, Providence Journal and other publications and websites.