‘Throwaway’ Pets Wreaking Havoc on Water Quality
The problem likely started with the dumping of these pets into ponds, and once in the wild, they can grow to the size of a football.
STORY AT-A-GLANCE
Cities across the U.S. are struggling with goldfish that have been dumped into lakes by their owners
In the wild, goldfish quickly “turn from pet to pest” and may wreak havoc on water quality and outcompete other species for resources
Goldfish, known scientifically as Carassius auratus, are a surprisingly hearty species, capable of living for 25 years or more and surviving harsh winter conditions
As they feed, they can uproot plants and disturb sediment, altering water quality and causing algal blooms
In Carver County, Minnesota, up to 50,000 goldfish were removed from the Grace Chain of Lakes on one day in October 2020, and officials are still trying to figure out how to get the goldfish population under control and restore the lake’s ecology and native fish population
Goldfish are one of the most innocuous pets you can care for, as they’ll happily swim in their tank — provided you’ve given them plenty of space, filtered water and environmental enrichment — without making so much as a peep to disturb you. In the wild, however, goldfish quickly “turn from pet to pest”1 and may wreak havoc on water quality and outcompete other species for resources.
Burnsville, Minnesota is just one city struggling with goldfish that have been dumped into lakes by their owners. These small, aquarium-sized fish don’t stay that way once in the wild. Given the chance, goldfish can grow to be the size of a football, and in Virginia, one fisherman set a record when he reeled in a 16-inch goldfish from the area.2
Why It’s Illegal to Dump Goldfish in Lakes
A goldfish owner may assume that dumping an unwanted fish into a nearby pond or lake is a humane option, but it’s illegal to dump fish into such water bodies for a reason. “A few goldfish might seem to some like a harmless addition to the local water body — but they’re not,” wrote the Minnesota Department of Natural Resources.3
“Goldfish are in the minnow family and can work their way through city stormwater ponds and into lakes and streams downstream with big impacts, by rapidly reproducing, surviving harsh winters, and feeding in and stirring up the bottom like their close relatives, the common carp.”
Goldfish, known scientifically as Carassius auratus, are a surprisingly hearty species, capable of living for 25 years or more and surviving harsh winter conditions. However, as they feed, they can uproot plants and disturb sediment, altering water quality and causing algal blooms.
Speaking with The Washington Post, Caleb Ashling, Burnsville’s natural resources specialist, said, “Goldfish have the ability to drastically change water quality, which can have a cascade of impacts on plants and other animals. They are a major concern.”4
‘Wild’ Goldfish Populations Out of Control
As part of the carp family, goldfish can travel into lakes and streams downstream, and with their rapid rate of reproduction,5 quickly become out of control.
In Carver County, Minnesota, up to 50,000 goldfish were removed from the Grace Chain of Lakes on one day in October 2020, and officials are still trying to figure out how to get the goldfish population under control and restore the lake’s ecology and native fish population.6
The Grace Chain of Lakes connects to the Minnesota River, and the concern is that the goldfish may continue to spread, “and there may be hundreds of thousands of them.”7
“The most likely reason for the goldfish presence is one or more individuals illegally dumped pet goldfish over the years,” according to the county.8 In another instance in Eagan, Minnesota, goldfish populations also grew out of control after someone dumped their unwanted goldfish into a pond. The Minnesota Department of Natural Resources reported:9
“After two or three years of attempted goldfish removals and alum treatments, the fish remained, most of them 6 inches or less. Getting the orange invaders out took a lot of effort and expense.
‘We tried netting them out,’ [Eagan water resources specialist Jessie] Koehle says, ‘and we got thousands of them, but we couldn’t get them all. Eventually we had to use rotenone to reclaim the pond, killing all the fish and starting over.’
The pond’s water is again clear and native plants are thriving, but the whole episode could have been avoided if the goldfish owner had taken more care in disposing of the fish.”
In addition to goldfish, other ornamental or pet fish such as koi, pacu and piranhas have also been found in Minnesota waters where they don’t belong.10
Do Your Research Before Getting a Fish for a Pet
Fish are often considered to be “throwaway” pets that require little to no commitment, but they require specialized care, including attention to food preferences, water temperature, adequate filtration and even current speed in the tank. Further, they have cognitive abilities that “match or exceed other vertebrates,” making them worthy of “the same level of protection as any other vertebrate.”11
If adding a fish to your home, be sure to provide hiding spots and places to explore in the tank, and research which fish species make suitable tank mates. While some fish only live a few years, you should you be prepared to care for your fish for decades if you choose a goldfish or koi, including visits to the veterinarian, especially if your fish seems sick or “off.”
If you can no longer care for your fish, under no circumstances should they be dumped into a local pond, lake or stream. Instead, search for a fish rescue in your area, which will take in unwanted pet fish and other aquatic species.
Healthypets Disclaimer: This information is for educational purposes only and is not intended to replace the advice of your own veterinarian or doctor. Dr. Karen Becker cannot answer specific questions about your pet's medical issues or make medical recommendations for your pet without first establishing a veterinarian-client-patient relationship. Your pet's medical protocol should be given by your holistic veterinarian.