Confined to a small bowl, goldfish remain rather miniscule. But turned loose in open water and the pet fish can grow to be several inches long.

That's what happened in Teller Lake No. 5, a neighborhood lake near Boulder, Colorado, where thousands of goldfish have proliferated and begun crowding out native species. Local wildlife officials are concerned the invaders could unsettle the lake's ecological balance.

"Goldfish are not a native species and are very harmful to the local aquatic ecosystem," Kristin Cannon, Boulder's district wildlife manager, said in a statement. "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."

Officials say the goldfish invasion most likely began when a handful of the pets were dumped into the lake. Two to three years later and those four or five fish have turned into 4,000.

"Dumping your pets into a lake could bring diseases to native animals and plants as well as out-compete them for resources," Jennifer Churchill, a Colorado Parks and Wildlife spokeswoman, told ABC News. "Everything can be affected. Non-native species can potentially wipe out the fishery as we've put it together."

A similar episode happened at nearby Thunderbird Lake in 2012. Wildlife officials were forced send pulses of electricity through the water while boating around and scooping up the momentarily incapacitated fish. They collected nearly 3,000 goldfish. Officials will likely execute a similar operation at Teller Lake No. 5.

"[The boat] has little pointers at the front with electroshock. It stuns the fish. It doesn't kill them. They get stunned and they float to the surface and we can collect them," Churchill explained to KUSA-TV.

The collected fish will be used to feed the birds at a local raptor rehabilitation center.