[TOMT][MOVIE] Scuba underwater sex and killer woman

I remember seeing a movie (normal movie not porn) many years ago (it's probably a movie made before '2000) where there was a couple having sex underwater dressed with scuba gear and the woman at some point cut the air tube of the man and drowned him. I don't know if it was some kind of black widow type movie, but I couldn't find any info. Any idea on the title? Thank you.