This isn't the first time that goldfish have become a problem for Colorado waterbodies. In 2012, Colorado Parks and Wildlife stunned and removed hundreds of koi from Thunderbird lake. While they didn't remove all of the koi, some are still being spotted, they are deemed to be at an acceptable population level.
|goldfish (Carassius auratus) by U.S. Geological Survey Archive, U.S. Geological Survey, Bugwood.org|
Daily Camera Boulder News: Non-native fish may mean draining one Boulder lake, monitoring at another
Department of Natural Resources press release: Invasive goldfish dumped at Teller Lake #5 in Boulder