Here are some possible scenarios:
* Typo: You might be thinking of a different movie with a similar title. Do you recall any other words from the title, or maybe the genre of the film?
* Indie Film: It's possible that "Reef" is the title of a less-known independent movie. If you have more details (like the year it was released, the actors involved, or a plot description), that might help identify it.
* Documentary: Maybe you're thinking of a documentary about reefs. There are many documentaries about coral reefs, the ocean, and related topics.
To help me understand your question better, please provide any additional details you can recall about the movie.