Here is the full list of all 14 Luna's Fishing Garden achievements. It takes around 2-3 hours to unlock all of the achievements on Windows.
Plant 15 lotuses
Clean up the archipelago
Catch every fish
Catch an oarfish
Feed Sam avocados
Build 10 bird nests
Help Gustav rebuild a bridge
Find Poppy in a cave
Use balloons 3 times
Complete any of Nigel's field journals
Catch the same fish 3 times in a row
Jump off the island into the ocean 3 times
Catch every fish in one spot
Fail to catch 10 fish