Teller Lake, a small body of water along the eastern edge of Boulder, Colorado, United States, will likely need to be drained as thousands of goldfish have invaded. The lake’s ecosystem has been devastated as the population of goldfish has exploded from the handful that were cast into the lake two years ago.

Officials with Colorado Parks and Wildlife (CPW) said that the four or five discarded forsaken pets reproduced rapidly, ultimately becoming the current population of 3,000 – 4,000. The district wildlife manager in Boulder, Kristin Cannon, pointed out that, because Carassius auratus auratus are not native to the lake that they “are very harmful to the local aquatic ecosystem.”

Adding fish to bodies of freshwater is not encouraged, she said. “It is bad for our environment,” she said, “as well as illegal.” Jennifer Churchill, a spokeswoman for CPW, reported that the now-threatened population of native fish in Teller Lake include blue gill catfish, channel catfish and sun fish.

It was two and one-half years ago that wildlife officials went about removing over 2,000 invasive domesticated carp (also known as koi) from another Boulder lake. This was done by “electrofishing,” a common survey method of stunning fish before they are caught.

When executed correctly, electrofishing results does not harm fish permanently, returning fish to their natural state of consciousness within two minutes. Wildlife officials say electrofishing may also be done at Teller Lake. They are also thinking about draining the entire lake.

Ken Kehmeier is a senior aquatic biologist with Colorado Parks and Wildlife. He said that the “far-reaching effects of introducing exotic species to the environment” is not understood by most people. He said that native populations can be devastated under such scenarios, thanks to unbalanced competition and outbreaks of diseases. He said that the issue is one “anyone concerned with our environment should know about.”