Overview
Blood Beach is a 1981 American horror film written and directed by Jeffrey Bloom and starring David Huffman, John Saxon, and Burt Young. The premise, conceived by Steven Nalevansky, involves a creature lurking beneath the sand of Santa Monica Beach that attacks locals and vacationers. The film's tagline is: "Just when you thought it was safe to go back in the water—you can't get to it."
Plot
In the opening scene, a woman named Ruth is walking her dog on Los Angeles, California's Venice Beach, and is suddenly pulled under the sand of the deserted beach by an unseen force. The woman's screams for help are heard by Harry Caulder, a harbor patrol officer who is swimming nearby. Harry reports Ruth's disappearance to two LAPD detectives, Royko and Piantadosi, who claim that without a body, there is little they can do. The next day, Ruth's estranged daughter, Catherine, arrives from San Francisco after Harry calls her regarding her mother's disappearance.
Meanwhile, the mysterious and crazed Mrs. Selden, who resides in an abandoned section of the Santa Monica Pier, witnesses the attack and disappearance (and others throughout the film), but does not come forward.
That night, while staying in Ruth's house, Catherine hears Ruth's dog barking on the beach near the location where Ruth disappeared. Catherine investigates and finds the dog beheaded, near a small sinkhole. Royko and Piantadosi, as well as Harry, are called to the scene, but police pathologist Dr. Dimitrious cannot accurately determine a cause of death for the dog. Royko and Piantadosi believe it to be the work of a serial killer, due to reports of other disappearances over the past few months.
From Wikipedia (CC BY-SA 4.0).