Slack Bay (2016) on Netflix

In the early 20th century, at the Pas de Calais, people mysteriously disappear as Ma Loute, son of the local fishermen family, and Billie, daughter of the snobbish Van Peteghems, fall in love each other.

Summer 1910. Several tourists have vanished while relaxing on the beautiful beaches of the Channel Coast. Infamous inspectors Machin and Malfoy soon gather that the epicenter of these mysterious disappearances must be Slack Bay, a unique site where the Slack river and the sea join only at high tide. There lives a small community of fishermen and other oyster farmers. Among them evolves a curious family, the Bréfort, renowned ferrymen of the Slack Bay, lead by the father nick-named "The Eternal", who rules as best as he can on his prankster bunch of sons, especially the impetuous Ma Loute, aged 18. Towering high above the bay stands the Van Peteghems' mansion. Every summer, this bourgeois family - all degenerate and decadent from inbreeding - stagnates in the villa, not without mingling during their leisure hours of walking, sailing or bathing, with the ordinary local people, Ma Loute and the other Bréforts. Over the course of five days, as starts a peculiar love story between Ma Loute and the young and mischievous Billie Van Peteghem, confusion and mystification will descend on both families, shaking their convictions, foundations and way of life.

—Memento Films