Goldfish in a tank or backyard pond are good. Thousands of exotic goldfish taking over an entire lake is not just bad, it's an ecological disaster.

The Colorado Parks and Wildlife Department first noticed the non-native exotic fish in Teller Lake #5 a few weeks ago. Now, the fish number in the thousands and will have to be removed.

Kristin Cannon, district wildlife manager for Boulder says,

Goldfish are not a native species and are very harmful to the local aquatic ecosystem. "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."

The Colorado Parks and Wildlife Department is trying to determine who illegally dumped the goldfish into Teller Lake #5 and is asking anyone with information to contact them.

This goldfish invasion is similar to another in 2012, where wildlife officials removed over 2,200 non-native koi goldfish from Thunderbird Lake in Boulder. That infestation threatened the lake's entire ecosystem.

[Colorado Parks and Wildlife]