The domestic goldfish Getty Images

Environmental officers in Canada have launched a campaign to stop people from flushing their goldfish down the toilet, after the invasive species have been surviving - and multiplying - at a "scary" rate.

Officials in Alberta province, in western Canada, say they've found goldfish the size of dinner plates in stormwater ponds, where they run the risk of upsetting fragile ecosystems.

"It's quite surpris[ing] how large we're finding them and the sheer number," Alberta Environment and Parks official Kate Wilson told CBC News, which reported that in one case 40 domestic fish were found in a stormwater pond.

"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," she said.

"Approximately a third of invasive species out there that threaten native aquatic environments are from aquariums and the ornamental trade."

In order to combat the growing threat, officials have launched the "Don't Let It Loose" campaign, which aims to educate Albertans about the dangers domestic fish pose to the wild - even from beyond the grave.

"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," Wilson told Fort McMurray Today.

Wilson says the campaign will target pet stores, pet owners, and spiritual groups that release captured animals as an act of good karma.

According to Wilson, Alberta has also had sightings of another invasive species - the Prussian carp.

"Something weird is happening," she said. "It could be a group of people from somewhere else who are used to fishing for these kind of species which intentionally introduced them, which is highly illegal."