When it comes to a frightening setting for a movie, there's no question that bodies of water usually make big splashes with moviegoers.

Think about it: Apart from that obvious fear people have of drowning, it's not too difficult to get stirred up about what's swimming below you. The fear of the unknown, after all, is a very powerful thought.

If you like to dive into underwater horror thrillers, then you're in luck, since the "Piranha 3D" sequel "Piranha 3DD" is now in theaters. Plus it stars David "The Hoff" Hasslehoff. Does it get any better than that?

But before you apply your sunscreen and head off to the big-screen beach, you should familiarize yourself with some of movie's greatest underwater villains.

No. 5: The Gillman from "Creature from the Black Lagoon"

It wouldn't be right to do a list of great underwater villains without including the granddaddy of sea monsters, simply known as the Gillman.

Introduced in 1954, this prehistoric half man/half fish also had a heart. One half of it had a huge crush on the gorgeous leading lady (Julie Adams), yet the other half -- the dark side -- didn't think twice about dispatching any other humans he encountered.

True, the Gillman isn't the scariest villain to ever emerge from the waters, but he's certainly one of the most memorable. Besides, he's one of the coolest-looking movie monsters -- ever.

There were three "Creature" movies overall, and the second one, 1955's "Revenge of the Creature," is also notable because it featured a young, unknown actor named Clint Eastwood in a brief role as a bumbling lab assistant who loses a lab rat (it crawled up his sleeve). Now that's scary.

No. 4: Piranhas from "Piranha"

Following a certain classic film featuring a great white shark in 1975, oceans, lakes and streams proved to be a fertile breeding ground for any moviemaker trying to cash in on the underwater predator craze.

Enter B-movie king Roger Corman, who in 1978 unleashed a school of sharp-toothed fish down a river that were far more than your average ankle-biters. In the horror romp, "Piranha," Corman, along with director Joe Dante (who went on to helm "Gremlins"), invented a strain of piranha fish that were not only able to survive in rivers, but devoured everything -- especially humans -- in sight.

Of course by today's standards, "Piranha" screams low-budget (a Corman staple), but it doesn't really matter: Once the seed was planted in your mind, trying to forget the idea of killer fish in your local lake or river is a thought akin to swimming upstream against a fast current.

No. 3: Orca the killer whale from "Orca"

Forget about "Free Willy," this whale tale (another '70s flick inspired by that shark movie) has some serious bite.

Unlike Roger Corman's "Piranha," there was nothing to laugh about with this 1977 man vs. nature tale, where a big sea-hunter (Richard Harris) becomes the hunted after he kills the mate of an Orca whale. Of course, like any other films of the era, "Orca," technically, feels dated -- but it's thrilling nonetheless.

In an honorable mention in the killer whale department, Monstro the Whale from "Pinocchio" simply can't be ignored. Just because it's an animated Walt Disney family film, there's no denying that Monstro is a frightening creature to kids, especially when Pinocchio, Geppetto and Jiminy Cricket attempt their escape from the belly of the beast -- and that's no lie.

No. 2: Killer mermaids from "Pirates of the Caribbean: On Stranger Tides"

The best movie scenes are the ones you don't see coming, and the payoff is big in that regard in the fourth "Pirates of the Caribbean" in 2011.

It starts with creepy build-up, where a group of drop-dead gorgeous mermaids (are there any other kind?) enchant a group of unsuspecting victims in song. But even the ominous atmosphere can't prepare you for what comes next -- an unforgiving attack on a band of scallywags.

Plain and simple, what director Rob Marshall does with the mermaids in "On Stranger Tides" is groundbreaking (or water-breaking?), especially for a Disney movie.