Continuing my look at underwater movies.
Here's an ad for James Cameron's The Abyss starring Ed Harris, Mary Elizabeth Mastrontonio and Michael Biehn. It's about a group of deep sea divers and oil drillers that discover they aren't the only thing inhabiting the bottom of the ocean. The effects in this movie, particularly the water tentacle, were done by ILM and were what convinced George Lucas that the tech was there to start development of the Star Wars prequels.
See more underwater movies here.
See the Trailer: