Adelaide residents are being urged not to release noxious koi carp or their unwanted goldfish into the River Torrens, following sightings of more than a dozen suspected koi at Hackney, and a smaller number upstream at Dernancourt.

Koi are considered a noxious species under the SA Fisheries Management Act and cannot be owned without a permit from the Minister for Primary Industries.

It is illegal to dump koi, goldfish or any non-native fish, into South Australian rivers and people can be fined up to $120,000 for doing so.

so they had them as pets presumably, they had enough of them or the person that had them passed, or was moving and just dumped an invasive species into the river. What sort of arsehole does that ?