Here's a lesson in just how harmful it can be to "release" unwanted pets into the wild: A Colorado lake has been taken over by 3,000 to 4,000 goldfish after just a few of them were dumped there by careless pet owners, reports ABC News. The entire ecosystem of the lake is now threatened, and extreme measures may need to be taken to completely remove the invasive goldfish.

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

Teller Lake #5, a body of water near Boulder, was once home to thriving populations of channel catfish, blue gill fish and sunfish, but over the course of two years, the goldfish have almost completely pushed these other species out, as you can see in the photo below. Officials believe the goldfish spawned from just four or five individuals. It doesn't take much to throw an entire ecosystem out of whack. 

goldfish infested lake in Colorado

Removing thousands of goldfish from the lake won't be an easy task. (Photo: KMGH/ABC News video)

Releasing unwanted goldfish isn't only bad for the environment, it's also illegal. Wildlife officials are doing their best to track down the people responsible, but they will likely need someone to come forward with information. For now, they just want to make sure this sort of thing doesn't keep happening.

In the meantime, they are focusing on how to eradicate the goldfish and replenish the lake's previously stable ecosystem. Unfortunately, the only options left are severe. Either the lake will have to undergo "electroshock" treatment, effectively electrocuting all the goldfish (as well as any other animal currently residing there), or draining the lake. 

"With electroshocking, you go in the boat and stun the fish to paralyze and collect them," Churchill said, adding that the shock doesn't kill the fish. "The fish could also be collected if the lake is drained."

Neither of the two options are ideal, but they will allow officials to restock native fish at healthy levels — essentially rebuilding the ecosystem back from the ground up. All the collected goldfish will then be used to feed raptors at a local rehabilitation center. 

Related on MNN: