Keven, if you look back at the many previous posts on this subject, I think that many people will disagree with you. While anything is possible, birds bringing fish eggs on their feet is one of the least likely.
The most likely is fish swimming upstream during a flood. The next most likely is someone putting fish into the lake. It seems like the urge to put fish into a water that doesn't seem to have any is almost overwhelming.
It really doesn't matter how fish get into our lakes, what matters is what we do about it. That's where management comes in.