The Rift (1989 film)

The Rift Endless Descent is a 1990 film directed by Juan Piquer Simn and starring R. Lee Ermey involving a submarine rescue that goes awry. It is one of many underwaterthemed movies released around 1990, including The Abyss, Leviathan, DeepStar Six, The Evil Below and Lords of the Deep.

They trace the Siren Is black box to an underwater rift where they discover that the company they are working for has been engaged in illegal genetic engineering experiments that have produced a number of different mutant creatures.

Source: Wikipedia