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