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