Releasing my turtles?

I released my turtles in a pond that's at a park. i didn't think this was all that bad of an idea because the pond is really calm and it has a few of other turtles living there. i think its a man-made pond and there are very few fish there and ducks. people come by a lot and throw food into the water to feed the ducks and turtles so i didn't think food was to much of a problem, but everywhere i read that releasing a turtle into the wild is a bad idea and i know in my heart it is, but what is the chance of my turtles living in this kind of environment?