Cast 30

1. 

   John Agar

   Prof. Clete Ferguson

2. 

   Lori Nelson

   Helen Dobson

3. 

   John Bromfield

   Joe Hayes

4. 

   Nestor Paiva

   Captain Lucas

5. 

   Grandon Rhodes

   Jackson Foster

6. 

   Dave Willock

   Lou Gibson

7. 

   Robert B. Williams

   George Johnson

8. 

   Charles Cane

   Police Captain

9. Loretta Agar

   Woman on Boat (uncredited)

10. 

    Bill Baldwin

    Patrol Boat Dispatcher (voice / uncredited)

11. Jere Beery

    Photographer (uncredited)

12. Ricou Browning

    The Gill Man (in water) / Lab Technician (uncredited)

13. 

    Diane DeLaire

    Miss Abbott (uncredited)

14. Mike Doyle

    Cop (uncredited)

15. 

    Clint Eastwood

    Jennings (uncredited)

16. Jack Gargan

    Skipper (uncredited)

17. Charles Gibb

    Cop (uncredited)

18. 

    Brett Halsey

    Pete (uncredited)

19. 

    Don C. Harvey

    Mac - Spotlight Party Leader (uncredited)

20. Tom Hennesy

    The Gill Man (on land) / Marineland Diver (uncredited)

21. Don House

    Diver (uncredited)

22. 

    Robert F. Hoy

    Charlie (uncredited)

23. Ned Le Fevre

    Newscaster (uncredited)

24. Sydney Mason

    Police Announcer (uncredited)

25. Robert Nelson

    Dr. McCuller (uncredited)

26. Patricia Powers

    Girl in Convertible

27. 

    Bert Stevens

    Search Party Member (uncredited)

28. Charles Victor

    Policeman (uncredited)

29. Robert Wehling

    Joe (uncredited)

30. James R. Wolfe

    Man at Tank (uncredited)

Troupe 32