That doesn't really explain how they know to find this place, decades after the last time any member of their species visited it. It explains why evolution selected for this behavior, but the more interesting part is how it happens in an individual salmon.

>That doesn't really explain how they know to find this place, decades after the last time any member of their species visited it.

Because that's not what happened. These fish managed to get there because it was a good place for them to go, not because they were 'returning' to a place they had been before. The 'return' in the title is more about the fact that they are coming back to fill a niche in an area fish were blocked from, not that these specific fish were returning to a place they had been before. It almost seems like they were intentionally muddying the waters with the language used.

Clearly, the story that salmon go back to spawn and their birth pool is not 100% true

They don't. They knew how to find the river already, they just went further up the river now the dam had gone. This is no great feat of navigation, to follow the river until you find nice gravel to spawn in.

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.

This is total and complete speculation, but possibly some sort of genetic or epigenetic driven system favoring some sort of chemical gradient/fingerprint unique to each river, maybe?