Not only that, it looks like most of the stunt work done in the film was practical. In an interview with ET Canada, Kristen Stewart talked about her experience starring in the film.

Underwater follows a crew of aquatic researchers who have to get to safety after an earthquake devastates their subterranean laboratory. Unfortunately, there’s something horrifying lurking around the ocean seabed. Kristen Stewart, who plays the lead in the film went on to discuss a little bit more about the story.

Underwater  Kristen Stewart Discusses Story and Practical Effects Used - 67