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