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People tossed a few pet goldfish into a lake, and now they're taking over the ecosystem and growing to massive sizes

Erin Brodwin

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goldfish lake

(The goldfish-infested waters of Teller Lake near Boulder, Colorado.Colorado Park and Wildlife)

If you've ever dumped a pet goldfish in a nearby body of water and thought your act was harmless, think again.

The seemingly innocent creatures are wreaking havoc on ecosystems around the globe.

In April 2015, Colorado Parks and Wildlife officials faced an infestation of 4,000 goldfish in a lake in Boulder County a few years after someone was believed to have dumped a handful of pet goldfish into a nearby lake.

In 2013, wildlife officials in California reported that the fish had begun taking over Lake Tahoe, likely after pet owners had tossed them there.

And for the past 12 years, goldfish populations have been surging in the Vasse River in southwestern Australia, where researchers say the public's well-intentioned disposal practice is a big part of the problem.

goldfish lake!

(Teller Lake has thousands of goldfish.Colorado Parks and Wildlife)

The problem is not just that tons of tiny goldfish are in streams where there previously were none — the fish are also growing to massive sizes, in some cases getting as big as 4 pounds, according to Dr. Stephen Beatty, a professor at Murdoch University who has been leading research on how best to address the problem in southwest Australia.

He and his team members regularly found goldfish weighing about 2 pounds, they told Australian radio station 720 ABC Perth.

In Lake Tahoe, US Forest Service fish biologists reported being well acquainted with the supersized fish, which often weighed several pounds and measured between 4 and 8 inches.

giant fish 2

(Murdoch University)

In each case, local dumping appears to play a serious role.

"Perhaps they were kids' pets where the family have been moving house and their parents, not wanting to take the aquarium, have dumped them in the local wetlands," Beatty told 720 ABC Perth.

Since the goldfish are a nonnative species in these area, wildlife officials are concerned that they are threatening the natural aquatic ecosystem.

"It's a bad thing — it's a really bad thing," Colorado Parks and Wildlife spokesperson Jennifer Churchill told Fox 31 News last year. "They'll start eating up everything that the native fish and the amphibians and the birds are here to eat, and so that can have a really negative effect down the road — and this can kill this fishery in a few years."

teller lake skitch

But questions about how the populations grew to such massive proportions were still boggling scientists.

A paper that Beatty and his team published August 12 in the journal Ecology of Freshwater Fish found that goldfish, who were assumed to be pretty limited in terms of how far they could travel, can actually travel long distances to feed and forage, Mashable reported.

The researchers also found evidence that the fish are migrating to nearby wetlands and reproducing, which further fuels their population growth.

"Just letting go of a pet, no matter how innocuous you think it is in your aquarium or how pretty it is, can potentially cause a lot of damage," Beatty told Mashable.

Amanda Macias contributed reporting.

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