The bizarre plea to stony-hearted pet owners has been issued in the province of Alberta, where environmental officers say the fish are multiplying at an alarming rate in storm ponds. Forty fish were pulled from a single pond in the north of the province earlier this year.

“It’s quite a surprise how large we are finding them and the sheer number,” said Kate Wilson, from Alberta’s environment department, quoted on CBC News. “That’s really scary because it means they’re reproducing in the wild, they are getting quite large and they are surviving the winters that far north.”

Goldfish are considered to be an invasive species, and the government fears they could upset fragile local ecosystems. Now it has launched the ‘Don’t Let It Loose’ campaign to highlight the problems flushed pets could cause. “Even if the fish are dead they could have diseases or parasites that could be introduced, especially if the water treatment system is not top notch,” Ms Wilson told Fort McMurray Today.

The campaign will also be aimed at pet stores and markets, plus groups that engage in ‘mercy releases’ to set captive animals free.

Another invasive species spotted in Canadian rivers is the Prussian Carp. But Alberta has a good record in banishing non-native species, and has had no resident rat population for decades.