Different ways fish can enter a waterway?

I know the usual ways that fish get from place to place.

Fish outgrow an aquarium and the owner dumps them in a local waterway
People import fish and release them to try and farm them(ie. snakehead)and they start breeding and get out of control.
Floods or a wet season where fish can go from one place to another.
etc


Was cleaning out my pond and noticed 3 small fish in there that I know for sure that I didnt put them in. They are small(under an inch) and look like a sort of minnow.

The only thing that I can think of is that a bird was in a pond/lake drinking or eating and stepped into some fish eggs. The bird flies to my pond and the eggs fall off and hatch.

This is the only thing I can think of. When I told this to my friend, they kind of looked at me like I was dumb. Is this feasible?