Pond To A Creek/ Cold River

i fish this pond, that doesnt hold big bass, 2 lbs is the max. any way a cold stream run into it fill it up, then at the other it has a silo type thing filtering the water into a run off creek, then filtering in a river. i assume it is a river, some places look shallow like a creek, then have big deep holes. my question is,

following the river/stream to each of its holes, it has bass in it. how did they get there? did someone put them from the pond. i doubt the fish went threw the drain and flopped `100 yards to the river/stream. i hope my question makes since, in a nutshell a shallow river that has deep holes has bass and bluegill in em, i seen gills making beds. So if they are bedding, that mean they are substaining aswell, right?

this river/stream is also cold, almost like deep mountain trout stream.idk bass cold survive that 24/7