I am no longer going to worry about how fish inexplicably get into bodies of water. Whether they swam upstream or got washed downstream, came on a turtle's back or in a bird's stomach, were sucked out of a lake by a tornado or were abducted by aliens, if they arrived by an act of God or via a practical joke by a neighbor, if they were stocked by the innate perversity of the universe or by your In-Laws,
FISH HAPPEN
and we just have to deal with them.