this does happen but they cannot tolerate our winters, the cold water kills them... if you have a source of warm water though, they can survive, power plant or so...
when they had the fish farm on Brunners Island on the Susquehanna years ago they had many escape, large schools in the warm water, used lettuce balled up on a hook to catch them... was good eating for free, but when they shut the plant down for maintenance they were all killed...