Leviathan (1989) is a sci-fi film, following a line of movies like Alien (1979) and The Thing (1982), depicting encounters of a group of humans with a ravenous orgamism of an unknown origin. This one takes place deep under water, where an American mining expedition uncoveres a mutant creature, that settled on board of an old Soviet wreck.
Movie stars Peter Weller and Amanda Pays. It had been considered mediocre almost universally, yet worth a typical night movie.
It is one of many underwater-themed movies released around 1989, including The Abyss, Deepstar Six, The Evil Below, Lords of the Deep, and The Rift (Endless Descent).