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