The owner of shepherds fish farm in Acadians parish in louisiana told me that green sunfish are excellent at swimming upstream and could have definitely entered that way.

In my opinion I would not start over. I worried about the same thing when it happened to me. But my pond is five years old now and we rarely catch any eating size GSF. After tasting them I had hoped the pond would get GSF heavy but no such luck. I don't think you have anything to worry about. I'm no expert but I have heard some of the experts talk about it with mixed reviews. But from my own experience, they don't reproduce enough to out number the bream, plus you have bass to control them. I used to worry about this, and so I used to trap as manny as I could and remove them, I now realize that worrying and trapping was unnecessary.

3rd acre fertilized fed and aerated