I think a lot of people underestimate the capability of a high water event for stocking fish. That "ditch" that runs into one end of the pond becomes a highway when a 100 yr rain occurs.
I'm also in agreement with Dave on the hatchery issue. Mix ups and unintended hitchhikers are fairly common occurrences. The careless, traveling fishtruck scenario appears to account for the majority of those. Buy your fish from a reputable source, and hand sort as you stock.
For proof that bucket stocking occurs, we need look no further than canyoncreek's thread. He himself stated that had he not discovered the interloper, he would've been inclined to go with the bird delivery explanation when he caught a bullhead that he never stocked.
Unless we spend 24 hours a day, 7 days a week, 365 days a year standing in front of our ponds, how do we know that bucket stocking hasn't happened? We may think our ponds are secure, but in reality we probably don't know that for a fact.
I have no doubt that a bird can drop a fish while in flight. But in the scenario we are discussing here, ( ponds full of smaller bluegills), it needs to happen at least twice. Once with a male, and another time with a female BG. And both fish need to survive, and reproduce.
