Temtem is full of small side quests to complete in order to obtain various rewards. Check out the complete guide to Turquesa Ferry.
Please note that this quest requires Surfboard to be completed in full.
Where to find the Ferry to Turquesa quest
This quest is located in Briçal de Mar, on one of the pontoons on the water's edge (right). You have to talk to Theodora. She will ask you where the ferry that was supposed to take her to Turquesa is. You'll have to investigate.
Step One: Talk to the Riverine Community
This stage is only accessible after beating Sophia and getting the Surfboard. You'll then have to go to Turquesa (just south-east of Deniz). You have to talk to different people in order to gather information.
Talking to Giada
Giada is next to the house circled in red on the map below.
Talking to Jana
You will find Jana in front of the bar she runs (the Sirokos). In Early Access, this bar is closed but Jana is available and you can talk to her.
Step 2: Find the Ferry
The ferry unfortunately crashed in the open sea. Here's its location:
It's completely destroyed. You will have to report it to Idris. He will offer you 2 Revive.
Last step: Warn Theodora
After this long journey, all you have to do is go back to Theodora in Briçal de Mar to explain the situation to her. She will offer you 3 Smoke Bomb.