In order to survive, you wouldn't want to be wiped out if your home stream vanished. You'd want at least the likely chance of going to another stream to spawn and breed. Probably the salmon just swim upriver when they want to spawn. And it happened to be that now the Klamath is open.

Yeah, there's clearly tendencies for the fish to return to where they were born. I'm sure that's driven by all kinds of complex genetic memories and probably more importantly selective advantage due to adaptation to the specific characteristics of the given stream, but genetic memories for a specific stream seems a little bit unlikely.