system
Given the following post, respond as if you're commenting on Reddit:
human
How do fish naturally "spread" to other lakes/ponds?

For a little background to my question. My uncle bought a house with a decent piece of property. He dug a large pond that he has been intending to stock with fish for his grandkids, nieces and nephews. He dug this pond a couple of years ago, and has been letting the natural plants grow around it, balancing the PH, and just getting it suited for fish. 

A few days ago, he noticed several small pan fish around the edge of the pond. He didn't put them in, and his pond is pretty far from any roads or streets, and near his house, so it's very unlikely anyone dumped anything in. There is no water running in, and no floods connecting it to any other water. 

People on his Facebook have suggested birds of prey dropping them in, or even bears/cougars. Those seem relatively unlikely as I would think they would be unable to survive swim after being grabbed/dropped by a large predator. I'm unconvinced, any ideas?
gpt
The general hypothesis is actually not that the birds carry the fish themselves and drop them into a lake. It's that fish eggs in the water stick to the feet of birds, and they deposit the eggs into a new body of water when they fly somewhere else. To answer your question though we have no clue. There was a big study a couple years ago to look into this bird feet egg hypothesis that didn't disprove the idea but couldn't find any evidence at all that this actually happens in nature.