Here is the full list of all 51 Summer in Mara achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
The sea is dangerous, next time get back to your boat before getting tired.
Build all the main structures on Home Island.
Catch one fish of every type.
Sing the old Navy song on its base.
Visit all the islands from Mara.
Complete all the quests from Napopo.
Cook 50 dishes.
Unlock all the crops on Home Island.
Pay the mortgage on your boat.
Complete all the quests from Litio.
Defeat the Elit.
Recover all the chrystalis from the Door.
Complete all the quests from Pilly, Milly & Tilly.
Complete all the quests from Rigatta.
Complete all the quests from Taima.
Complete all the quests from Ecco.
Complete all the quests from Aquila.
Get all the Koa's outfits.
Complete all the quests from Blu.
Complete all the quests from Akaji.
Complete all the quests from Mûn.
Use the recycle bin 100 times.
Beat Ereti in a race.
Complete all the quests from Mayo.
Complete all the quests from Noho.
Complete all the quests from Awan.
Complete all the quests from Onzo.
Complete all the quests from Taka.
Get the boat to max level.
Get all the Koa's backpacks.
Get one farm animal of each type for your island.
Complete all the quests from Brram.
Cook 30 dishes.
Sell objects for a total of 3000 coins.
Meet Dunna.
Sell objects for a total of 2000 coins.
Craft 60 objects.
Unlock the mine.
Carry 99 oranges in the backpack.
Sell objects for a total of 1000 coins.
Craft 40 objects.
Read all the messages on Puni Cave.
Ask Caleb to take you back to Qälis.
Meet Saimi.
Cook 15 dishes.
Craft 20 objects.
Collect 90 objects.
Remember...
Wake up after the tutorial.
Collect 60 objects.
Collect 30 objects.