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