Torchy, what do you mean by not any flowing water. Do you fill it by well? Just because you don't have any water flowing in doesn't mean the trash fish aren't swimming upstream when the pond overflows. In my opinion, that is the most common way they enter. I found a green sunfish lying in a coastal field after a rain (which was wide and shallow during the rain) a half mile from a pond.
I'm not an expert by any means but I'm not sold on the bird and egg theory unless ponds are close together.
I have one pond that is close to a live creek and in four years it overflowed one winter when fish aren't active and I don't have any trash fish. I have another pond that doesn't overflow at all and in three years not a single trash fish.
Your pond being that new means that birds would have carried at least one male and female of two different species that lived to grow and reproduce. That's four fish in the first year.
Does anyone else have any ponds with unwanted species that are filled by well and no outflow and no helpful neighbors?
