Scientists surgically transform the Creature into an air-breather, but being able to live on land is not enough to make him comfortable with humans. Enraged, he turns his wrath on anyone who comes near as he desperately tries to return to the deep-water world where he truly belongs.
| Actor | Role |
|---|---|
 Rex ReasonDr. Thomas Morgan | Dr. Thomas Morgan |
 Jeff MorrowDr. William Barton | Dr. William Barton |
 Leigh SnowdenMarcia Barton | Marcia Barton |
 Gregg PalmerJed Grant | Jed Grant |
 Maurice MansonDr. Borg | Dr. Borg |
 James RawleyDr. Johnson | Dr. Johnson |
 David McMahonCapt. Stanley | Capt. Stanley |
 Paul FierroMorteno | Morteno |
 Lillian MolieriMrs. Morteno | Mrs. Morteno |
 Frank ChaseSteward | Steward |
| LLarry HudsonState Trooper | State Trooper |
 Ricou BrowningThe Gill Man (in water)(uncredited) | The Gill Man (in water)(uncredited) |
 Don MegowanThe Gill Man (on land)(uncredited) | The Gill Man (on land)(uncredited) |
 George SowardsRanch Hand (uncredited) | Ranch Hand (uncredited) |