It's a simple cruise from Australia to Asia to deliver a yacht. Luke (Damian Walshe-Howling), an experienced sailor, hires Warren (Kieran Darcy-Smith) as a crewman for the voyage, and he invites three friends -- pal Matt (Gyton Grantley), Matt's girlfriend Suzie (Adrienne Pickering) and Matt's sister (and Luke's ex-girlfriend) Kate (Zoe Naylor) -- to enjoy the trip.

It's all pretty idyllic ... until the yacht strikes a shallow reef and capsizes far from land. Luke thinks they can make the 10- to 12-mile swim to a small island they'd visited the day before, but Warren says the shark-filled waters are too dangerous and opts to stay with the sinking boat.

The others, after some debate, decide to try their luck with Luke. Clad in wetsuits and carrying minimal supplies and two small flotation devices, they set out into the vast ocean.

The story is loosely based on true events; although a great many details are changed, including the number of people involved, it involves similar circumstances and a similar outcome to the film. Suffice it to say, there's a shark.

There have been a lot of shark movies over the years, and this movie draws an immediate comparison to Open Water, which also pits people against the vastness of the sea.

This movie is better.

Where The Reef succeeds is in the tension it creates as our swimmers try not to give in to the obvious panic such a situation engenders. And once a shark arrives -- as you know it will, it's Australia after all -- can you even imagine the terror of trying to keep moving without knowing what's going on below the surface of the water?

The film also benefits by using genuine shark footage, not special effects, to great effect. Because director Andrew Traucki opts for a minimalist approach -- like Jaws, the shark is scarier in this case because it's mostly not seen -- that footage blends fairly seamlessly with the people in the water.

If you're looking for reasons not to swim in the ocean -- or sail more than a few hundred yards from shore -- watch The Reef. It's a tense, scary movie.