Yeah, but at least two live fish (a male and female) being dropped into the same remote lake, then finding each other at spawning time seems increasing implausible. Never say never, but ...

Apparently some fish species do have small sticky eggs that can stick to the legs of water fowl, or even (with very small probability) pass through them intact, so this seems much more likely. Maybe a group of ducks feeding in one place then flying off to another?