I've seen a lot of confusion about how to catch these things, so I just wanted to share my little experience for those who might still be uncertain of how and where to catch them.
So for the first half of September they appear at the second waterfall, the one that pours into the ocean, and as you can see by this screenshot, my town has a RIDICULOUSLY inconvenient placement for this.
They appear directly underneath the waterfall, so it's difficult to see if your town is arranged like mine.
I saw one just barely poking out and tried to get it to notice the line, but of course no good. So I moved up the hill and Cookie chose the worst time to ping and invite me to her house.
I placed myself on the edge of the cliff seen in the above photo, threw my bobber onto the waterfall and let it drop down and suddenly I hear the "plop" sound of a fish grabbing it.
You can just barely see it poking out to the right of the purple roses.
And sure enough...
Now all I need is the King Salmon, which I believe works the same way, only with a larger shadow, and my fish encyclopedia is done!
So for the first half of September they appear at the second waterfall, the one that pours into the ocean, and as you can see by this screenshot, my town has a RIDICULOUSLY inconvenient placement for this.

They appear directly underneath the waterfall, so it's difficult to see if your town is arranged like mine.
I saw one just barely poking out and tried to get it to notice the line, but of course no good. So I moved up the hill and Cookie chose the worst time to ping and invite me to her house.
I placed myself on the edge of the cliff seen in the above photo, threw my bobber onto the waterfall and let it drop down and suddenly I hear the "plop" sound of a fish grabbing it.

You can just barely see it poking out to the right of the purple roses.
And sure enough...

Now all I need is the King Salmon, which I believe works the same way, only with a larger shadow, and my fish encyclopedia is done!