Goldfish 3,000 Strong: Dumped Koi Raised an Invading Army in Colorado

An army of 3,000 strong and counting is building in a lake in Boulder, Colorado, and the potential impact of this invasive exotic fish has conservationists on edge.

The fish in question are koi goldfish - the vibrantly orange, white, and black fish that frequently fill the artificial ponds of homes and restaurants.

According to multiple local media accounts, a park ranger first noticed the clouds of an estimated 3,000 to 4,000 fish in Boulder's Teller Lake #5 a few weeks ago. News of the population explosion has since spread, and experts looking to the area are growing concerned.

That's because, "nonnative species can be devastating to native populations by causing disease and creating competition unbalance," Kristen Cannon, Boulder's district wildlife manager, told ABC News.

"If they escape [the lake] and move downstream, they'll directly compete with our native species - all of which were here before the land was even settled - not only for spawning habitat but also for foraging resources," Ben Swigle, a fish biologist at the Colorado Parks and Wildlife (CPW), added in an interview with Live Science.

Swigle went on to explain that there are a handful of species already at risk in the immediate area, just downstream from where the invaded lake is. This includes the stonecat catfish, the common shiner, and the brassy minnow.

But how did such a massive koi army get there in the first place? (Scroll to read on...)

"Based on their size, it looks like they're 3-year-olds, which were probably produced from a small handful of fish that were illegally introduced into the lake," Swigle explained.

Essentially, they are not unlike the urban legend of flushed gators crawling around underground NYC. These dumped pond pets found themselves in habitat with few predators and plenty of food, allowing them to mass produce in a very short amount of time.

"We strongly encourage the public not to dump their unwanted pet fish in our waters. It is bad for our environment, as well as illegal," Cannon told ABC.

According to the Smithsonian institute, Boulder Parks and Wildlife officials will likely exterminate the fishy army before it can begin its march, likely by putting an electric current in the water - a tactic that was previously successful during another lake's invasion in 2012.

The lake will then be left to be recover, hopefully with the reintroduction of local fish and flora.

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