DeepStar Six (1989)

This deep sea adventure/sci-fi/horror/creature feature is part of the three headed monster of 1989 oceanic flicks that brought us more underwater action than any time in the history of filmmaking, we are of course talking about The Abyss (1989), Leviathan (1989), and DeepStar Six (1989)!  All of them had some crossover plot points, similar characters, and questionable science, but DeepStar Six was the only one of the bunch that had B.J. from B.J. and the Bear, so screw your Academy Awards James Cameron!  In this classic, we follow an underwater crew helping build an experimental nuclear base in the deepest parts of the ocean.  As the team begins to survey the ground around them to find out where is the best place to start drilling holes, they soon discover that the very ocean floor below them is hollow.  It's not JUST hollow either, beneath the thin layer of earth is a centuries old creature that is not only going to take out everyone on board their underwater base, but could even make its way to the surface and start killing everyone in sight!  The movie definitely delivers on the tagline that "Not All Aliens Come From Space... Save Your Last Breath to Scream!"  This one also has a pretty solid cast of 80s actors like Greg Evigan (B.J. and the Bear, My Two Dads), Nancy Everhard (who shows her ever-hard nips throughout this one!), and Nia Peeples (who gives us a view of her hard "Neeples", while she works out underwater!).  It's a classic that came out coincidentally around the same time as two other underwater classics, so definitely check it out with The Abyss (1989) and Leviathan (1989), in the same way you compare Armageddon (1998) and Deep impact (1998) or Tombstone (1993) and Wyatt Earp (1994).