I did check with the DPI (I'm in Oz) and was allowed to release my (excess) rainbows into the dam (and creek) as they are a local species 
But that's not the norm
We also seem to have non-native guppies in the waterways here that are likely released aquarium fish. Apparently they thought it was a good idea at the time, like the cane toad...

But that's not the norm

We also seem to have non-native guppies in the waterways here that are likely released aquarium fish. Apparently they thought it was a good idea at the time, like the cane toad...