My bet is bucket stocking. Even behind a locked gate. Unless you are at your pond 24/7 or have cameras viewing it, kids or helpful relatives will dump fish in it. I'd do some questioning of anybody that has access to your pond, and take a look at whomever lives in any houses within 1/2 mile (or more) of the pond. The less times that a pond owner is at their pond, the chances of bucket stocking gets higher.
I honestly have no idea how these fish got in there. I do have to say that I would believe that bucket stocking is the least likely though.
This pond is in my front yard behind a gate. My kids are home schooled, so my wife and kids are at home all day everyday and I have three large dogs outside. Anyone that would consider "helping out" with my stocking knows what I am trying to accomplish and would have to have someone at the house open the gate to let them in. I just don't think that happened.
With that said, I believe that Overton's is a first class fishery and that the odds of these fish coming from them is unlikely.
