Salmon is easy. It's at the waterfall, the one on the bottom by the beach, not the one on the top by the "wall". King salmon, if I remember correctly, is just a big fish in the river. It might be challenging since you could also catch an arapaima. King salmons can be caught anytime of the day. Hope I helped.
Ok, never mind about my above post. I just remember this one time I caught a kind salmon at the bottom waterfall. So op, both Salmon and King Salmon is at the waterfall by the beach.