Edgar's Review of Swimming Pool
Ohhh, this is the evidence I needed. Even if it's a movie of the 2000s, you can revive the absorbing and claustrophobic environment that invaded the thrillers of the 80s and early 90s. The swimming pool is a metaphor: all we see are the leaves and the dirt floating, and even if removed, we clearly see the surface and ignore what lies on the bottom. "The tip of the iceberg in thrillers", you could say about Ozon's movie, regardless of how young he directed it.
The twist is quite clear. The "you-can-interpret-what-you-want" law does not apply in this case; only the time frame of the twist varies in each person. For the sake of avoiding spoilers, though, it won't be written here.