Colorado Parks and Wildlife is battling an invasive goldfish army

This is why you should never release your pets into the wild.


Cynthia McKelvey

Internet Culture

Published Apr 8, 2015   Updated May 29, 2021, 3:02 am CDT

A Colorado lake has been overrun with a population of goldfish several thousand strong.

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The state’s Department of Parks and Wildlife thinks the school was seeded by a small handful of goldfish dumped into the lake a couple years ago. The fish, which apparently are the bunnies of the water, multiplied rapidly and now officials are concerned they may lay waste to the local ecosystem.

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There’s a number of ways that the goldfish can accomplish this mini-apocalypse. They can bring in foreign disease, throw off the pH of the lake, or eat all the food, just to name a few. That can be bad news for native fish species. And it can have a ripple effect that extends far beyond just one little lake. Birds and other migrating species may stop visiting the lake (or new ones may come to it), which would change ecosystems on the land as well.

Authorities are on the hunt for the people who supplied the initial goldfish infantry—because not only is dumping your house pet into the wild stupid, it’s illegal. This is far from the first time house pets let loose in the wilderness have caused a problem. Pet Burmese pythons set free in the Florida everglades wreaked so much havoc that in 2013 the state sponsored a contest for people to hunt the massive snakes. And let’s not forget that outdoor cats single-handedly kill several billion animals per year.

Invasive or non-native species are a common problem for ecosystems. Foreign animals are usually brought to a new location unintentionally by human activity, but there have been cases of new species introduced on purpose with disastrous results. Just take a look at the Asian carp problem threatening the Great Lakes. In a new environment, animals might lack the usual predators and competitors for food that keep them in check, giving them a chance to multiply at an astronomical rate. It can get so bad that the animal completely upends the ecosystem, to the point they can push out the animals and plants that used to live there.

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As you can imagine, once the invasion happens it’s difficult or impossible to reverse. So there’s not much an average Joe can do other than, you know, not release pets into the wild. 

But at least it’s something.

Photo via Pogrebnoj-Alexandroff/Wikimedia (CC BY 3.0)

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*First Published: Apr 8, 2015, 7:22 pm CDT