The City of Ottawa is set to euthanize a population of invasive goldfish found in a stormwater pond located in the Central Park neighborhood. The exact size of this population is still uncertain. In March, city workers removed approximately 5,000 dead goldfish from the pond in Celebration Park, using nets and manual collection methods. Recently, city officials reported discovering a new group of goldfish in the same pond. A rough visual assessment suggests that the surviving population may range from 500 to 1,000 fish.

Coun. Riley Brockington, who represents the area, expressed disbelief at the numbers. "The fact that we’ve had approximately 6,000 fish in this pond, in this year, is mind-blowing. It’s just a number that’s difficult for me to wrap my head around," he said.

Residents initially reported thousands of dead fish washing ashore in March, and now the councillor indicates that the goldfish have returned. Carleton University biology professor Steven Cooke warned that the city’s estimates might be low. "These are the kinds of fish that are extremely fecund — fancy word for they make lots of babies," he explained. Cooke noted that a single female goldfish can produce around 6,000 offspring annually, meaning that even a small breeding pair can lead to a significant population increase.

Cooke estimates that the actual number of goldfish could be in the millions, although most of these would be newly spawned and still small. Goldfish, originally from eastern Asia, are recognized as an invasive species in Canada and the continental United States. They have established populations in various locations, including Hamilton Harbour, which is experiencing a severe infestation.

In stormwater ponds, goldfish face few natural predators, allowing their populations to grow unchecked. This unchecked growth can displace native species and disrupt aquatic plant life by disturbing sediment in the pond. Cooke stated, "They wind up smothering, basically dominating the waters in which they’re introduced. They can be really quite devastating in these small systems."

The origin of the goldfish in the stormwater pond remains unclear. According to a city statement, the Ontario Ministry of Natural Resources and Forestry mandates the euthanization of all invasive fish captured in stormwater ponds. The city plans to continue using nets to collect the goldfish but will not drain the pond or apply chemical treatments.

While netting may help reduce the population, Cooke cautioned that it is not a foolproof method for complete eradication. "All you need to do is miss one male, one female, and then you’ve got a pair that are ready to start cranking out babies," he said. He suggested that a fish-specific pesticide would be the most effective way to eliminate the goldfish entirely, but noted that authorities often lack the necessary public support for such measures.

Cooke emphasized the importance of preventing similar situations in the future. He urged pet owners not to release their goldfish into the wild, stating, "The most important message from this is, let’s use this as a lesson and stop this from happening."