At the same time as finishing Storm King's Thunder, I also got the Angler of the Northern Sea achievement (catching/finding one of each type of fish in Sea of Moving Ice). I was inspired to go after it after getting Angler of the Soshenstar, though unlike the latter this one actually required a fair amount of work.
Basically I tried to go to a different fishing spot every time I got the daily fishing mission for several weeks, eventually using this guide by DDM's Realm to keep track of which locations I still had to revisit to get the last couple of fish I was still missing.
It was time-consuming, but I thought the amount of randomness and grind required was just right to not feel annoying. I've been displaying my new title with pride, as it stands for one of the rare accomplishments in this game that can't be bought or fast-tracked with real money (at least as far as I'm aware).