LOS ANGELES: More than 40 years ago, Americans were afraid to go into the water as "Jaws" scared the daylights out of a generation of ocean swimmers. Hollywood is hoping for a repeat this summer with the movie "47 Meters Down."

There have been more than 50 shark movies since Steven Spielberg made cinematic history with "Jaws" in 1975.

This year's shark movie, which will open in the US on June 16, takes place almost entirely under water.

Sisters Lisa and Kate -- played by Mandy Moore and Claire Holt -- are on vacation in the Gulf of California, and it becomes clear that they should avoid climbing aboard a flimsy boat belonging to Taylor (Matthew Modine).

They also probably should not get inside Taylor's rusty shark cage to plunge into the water and observe the predators up close.

Modine's character attracts the sharks by pouring blood into the water -- before the cage breaks away from the boat and drops to the ocean floor.

The two young women with little diving experience find themselves in the dark with less than an hour of air in their oxygen tanks -- surrounded, of course, by hungry sharks.

'Physically taxing'

"What I found far more terrifying is the prospect and premise of drowning, of running out of air," Moore told reporters.

"That's my biggest fear. That's far more terrifying than sharks, which are terrifying enough."

Director Johannes Roberts decided that once the women plunged into the ocean there was no need for scenes on the surface.

"I had no interest in going back to reaction shots with Taylor and the other boys on the boat," he said.

"Imagine if in 'Gravity,' you kept cutting to ground control. It would have killed the movie," he said, referring to the 2013 Oscar-winning film about astronauts stranded in space.

For the film, Moore and Holt therefore spent eight hours a day for eight weeks inside a six-meter deep water tank.

"47 Meters Down" was filmed mainly in sun-deprived Britain, far from Mexico's bright Pacific coast. A few scenes were made in the Dominican Republic.

"We didn't realize how physically taxing it was going to be, all that time under water," Moore said.

"In that sense we were kind of Guinea pigs because no one knew what effect eight weeks everyday under water would have."

An especially large diving mask was designed so viewers could better see Moore and Holt's facial reactions.

The actresses could communicate via a special radio set, but communication with the rest of the film crew was via hand signs, while the director's instructions were delivered through a speaker inside the water tank.

"I was pretty nervous," said Holt. "But we had great people taking care of us."