"Goldfish the size of dinner plates are multiplying like bunnies."

The Alberta government is launching a campaign this summer to stop people from flushing their aquariums down their toilets. Goldfish the size of dinner plates are multiplying like bunnies from Lethbridge to Fort McMurray, the province says...
In one case, the municipality of Wood Buffalo pulled 40 of the domestic fish species from 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," said Wilson.

Further details at CBC News