aka Creatures from the Abyss
How bad is it? It's pretty bad.
Should you see it? It has a fervent cult following, but I still say no.
Three stereotypical teen couples on the beach discover an abandoned research vessel, go on board and eat radioactive mutated fish, causing monsters to be formed (including one woman giving birth to a sort of fish-spawn egg mass). Two of the gross-out scenes are stolen directly from "Evil Dead II" (one of my favorite trash films). You'll want the cast to get killed and all but one are dispatched. Perhaps I was just not in the mood for this, because there are a lot of people who claim that this is a masterpiece of junk.