Luna Wedler was actually 16 years old during filming and director Lisa Brühlmann made sure she was actually not seeing anything during the blindfold scene.
Lisa Brühlmann previously directed Hylas und die Nymphen (2013), based on the Greek myth and painting of the same name. She said of her long-time fascination with nymphs/mermaids: "The mermaid has a sense of anarchy which was something that really fascinated me and I wanted to tell a story [about it]."
When Mia is first seen as a teen, she is wearing a sweatshirt that reads "Bluedenim."