Goldfish Invasions Hamper the Ecosystem

For approximately the past seven years, ecologists and fish biologists throughout North America have been raising alarm bells about goldfish overwhelming fresh bodies of water. Experts think that well-meaning human fish caregivers are releasing them and believing the act is the humane thing to do. Actually, it is inhumane to the fish, and misguided. Goldfish thrive, then invade, disrupt the ecosystem, and reproduce under the right conditions.

To get an idea of the enormity of the problem, researchers believe tens of millions of goldfish inhabit the Great Lakes. The Royal Botanical Gardens counted as many as two million large and small goldfish around Hamilton Harbor off Lake Ontario in Canada in 2015. During the same year, volunteers stunned 4,500 goldfish in Dragon Lake near Quesnel in British Columbia – the opposite side of the country. Four years later in the same province, recreational fishing was banned in Lost Lake to prevent goldfish outnumbering native fish. Colorado Parks and Wildlife believe that someone dumped four goldfish in North Teller Lake in Boulder County in 2013 and that population exploded to 4,000 in 2015. Problems with goldfish invasions have also been documented in Lake Tahoe, Washington State, New York State and Michigan.

Goldfish are omnivores and bottom feeders, which kicks up sediment. Couple the sediment with the abundance of waste goldfish excrete, and the net result can contribute to algae blooms. Additionally, they compete with native fish for food and habitat. Plus, with climate change causing warmer water and water quality now on the decline, they can thrive more easily than native fish.

Goldfish can grow, too. They have been recorded up to over four pounds and over 14 inches long. So, they are almost too big for birds of prey, who appear not to like them very much anyway. One biologist described their scales like armor, which also makes it difficult for potential predators to access.

Are we blaming the goldfish? Not in the least.

Goldfish are companion pets just like dogs, cats, ferrets, rabbits, guinea pigs, etc. People think goldfish are easier to manage until they realize the necessary upkeep and the size of tank needed that is humane for the fish.

The two morals of the story are: please do your homework before getting a fish or any companion pet; and, if you decide a fish would be a good addition to your home, please do not discard it.

We have included links here to various fish aficionado websites about caring for goldfish.

5 Best Goldfish Tanks: What To Know Before Buying

Goldfish Care Guide (for Beginners)

Goldfish Care Sheet

The Goldfish Tank

How Long Do Goldfish Live? 5 Ways to Increase Their Lifespan

How to Take Care of a Goldfish


Balcerzak, Natalia. “Goldfish Invasion Shuts down Angling on Lost Lake.” Terrace Standard, 27 June 2019, https://issuu.com/blackpress/docs/i20190627041907774.

“Boulder pond reeling from goldfish invasion.” Denver7, 6 Apr. 2015, https://www.youtube.com/watch?v=0Wtkg35fdik.

Correia, Cory. “B.C. Lake Infested with Hundreds of Goldfish Just Months after Pets Released into Wild.” CBCnews, CBC/Radio Canada, 15 Aug. 2018, https://www.cbc.ca/news/canada/british-columbia/pinecrest-lake-residents-goldfish-infestation-1.4785714.

Craggs, Samantha. “Discarded Goldfish Are Taking over Hamilton’s Harbour.” CBCnews, CBC/Radio Canada, 7 Jan. 2016, https://www.cbc.ca/news/canada/hamilton/headlines/discarded-goldfish-are-taking-over-hamilton-s-harbour-1.3394203.

Dalbey, Beth. “Tiny Goldfish Create Monster Problem When Released In Fresh Water.” Spokane, WA Patch, Patch, 26 Apr. 2018, https://patch.com/washington/spokane/goldfish-create-monster-sized-problem-washington-lake.

“Giant, disruptive goldfish taking over Canada’s waterways.” CBC/Radio Canada, 9 July 2019, https://www.youtube.com/watch?v=nAcaqfxhpGk.

Heck, Cheva. “Super-Sized Goldfish Pose Giant Problem for Lake Tahoe.” USDA, 21 Feb. 2017, https://www.usda.gov/media/blog/2013/03/07/super-sized-goldfish-pose-giant-problem-lake-tahoe.

Jensen, Adam. “Giant Tahoe goldfish sparks international interest.” Tahoe Daily Tribune, 26 Feb. 2013, https://www.tahoedailytribune.com/news/giant-tahoe-goldfish-sparks-international-interest/.

Magin, Kyle. “Giant Goldfish Indicates Big Problems for Lake Tahoe.” Tahoe Quarterly, 2013, https://tahoequarterly.com/environment/giant-goldfish.

Morse, Katie. “Warning after giant goldfish is found in the Niagara River.” WKBW, 19 June 2019, https://www.wkbw.com/news/local-news/warning-after-giant-goldfish-is-found-in-the-niagara-river.

Oliver, Kevin. “Monster goldfish are breeding in Lake Tahoe.” KCRA, 19 Feb. 2013, https://www.kcra.com/article/monster-goldfish-are-breeding-in-lake-tahoe/6402536.

Safer, Martin. “Aquatic Invaders of the Pacific Northwest: Carassius auratus auratus (Common Goldfish).” Olden Labs, University of Washington, 2014, http://depts.washington.edu/oldenlab/wordpress/wp-content/uploads/2015/09/Carassius_auratus_Safer_2014.pdf.

Taekema, Dan. “New Study Helps Track ‘Destructive’ Giant Goldfish Threatening Hamilton Harbour.” CBCnews, CBC/Radio Canada, 31 Mar. 2019, https://www.cbc.ca/news/canada/hamilton/goldfish-study-1.5076637.

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