L'arbre sous la mer (1985)

Based on a book by Nikos Athenassiadis titled A Naked Young Girl, this slight, uneven fantasy-romance takes place on an isolated Greek island with a unique, petrified tree -- a part of the reason why Mathieu, a geologist (Christophe Malavoy) has arrived to do some research there. Other than the boatman who ferries back and forth to the mainland, the island's only inhabitants are a fisherman and his very pretty daughter Eleni (Eleni Drogoumi). Eleni seems a bit different right from the beginning; on the one hand, she likes wandering around dressed only in a long shirt, and on the other, she has a penchant for swimming all night with the dolphins. When the usually arrogant geologist starts transferring some of his interest from rocks to Eleni's comings-and-goings, he wonders if there is not something fishy about her parentage.

Unfortunately the movie L'arbre sous la mer is not yet available on HBO Max.