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