Lt. Cmdr. John 'Twill' Twillinger
Gail MacKenzie
Dr. Jess Rogers
Jody Simms
Dr. Tad Johns
Lt. Robert 'Clem' Clemens
Sheriff Josh Peters
Sandy MacKenzie
Connie Blake
Seaman Fred Johnson
Sally
George Blake (lab assistant)
Mrs. Simms
Lewis Clark Dobbs
Seaman Wyatt (Radioman)
Seaman Morty Beatty
Monster Victim
Deputy Larry
Admiral Greenhouse
Deputy Scotty
Other Lock Watchman
Boy with Morty's Cap
Coroner Nate Brown
Gatekeeper
Patterson
Watchman at Lock 57
Seaman Howard Sanders
Davis - Resort Owner
Captain Masters
Deputy Brewer
Clarke