Young Richard Lindsay (Arnold Lessing) has given up his career in science in favor of his newfound passion, surfing on the Santa Monica beachfront near his father and stepmother's house, where he lives. This is to the great displeasure of his father, the noted oceanographer Dr. Otto Lindsay (Jon Hall), who is married to the younger Vicky (Sue Casey). Vicki is dissatisfied with Otto's relative lack of devotion to her. Also living with the Lindsays is Richard's sculptor buddy Mark (Walker Edmiston), who walks with a limp as a result of an auto accident Richard had earlier.
While Vicky hits on her stepson and teases his friend Mark, a monster emerges from the ocean and starts slaughtering the kids on the beach. Dr. Lindsay seems convinced that it is a genetically mutated carnivorous South American "fantigua fish" that has grown large enough in anthropomorphic manner to exist out of the oceans in loathsome seaweed-shrouded form.
The surfing footage used for the scene where Richard runs a film for Mark was shot by one of the most prolific surf filmmakers of the 1960s, Dale Davis, who produced Walk on the Wet Side, Strictly Hot, and the landmark The Golden Breed. For some release prints, the footage was printed in color.
According to the trailer for the film, the dancing girls seen in the movie are "The Watusi Dancing Girls" from Hollywood's Whisky a Go Go club on Sunset Boulevard.
Most of the interior shots - specifically all those of the Lindsay home - were shot at the Brentwood residence of Henry and Shirley Rose at 816 Glenmere Way in West Los Angeles. The Roses were friends of the producer, Edward Janis, with Shirley Rose also being the film's art director. The office scene was shot at the business office of Henry Rose.
All the sculptures and the 'Kingsley the Lion' puppet used in the film, were created by the actor who played Mark - Walker Edmiston, the host of "The Walker Edmiston Show", a children's television program in Los Angeles that featured puppets of his own creation including Kingsley the Lion.
The score for The Beach Girls and the Monster was arranged and conducted by Chuck Sagle, and a few of the musicians assembled for the soundtrack were members of the surf band The Hustlers (who are known for their songs "Kopout," "Inertia" and "Wailin’ Out") from Riverside, California. In the book, Pop Surf Culture, written by Brian Chidester and Domenic Priore, the soundtrack of The Beach Girls and the Monster "has got to rank up there among the best … no fewer than 13 different sections of full-bore, deep-reverb tank surf instrumentals throb the soundtrack."
The theme song, "Dance Baby Dance," was written by Frank Sinatra, Jr. and Joan Janis and produced by Edward Janis. Arnold Lessing, who plays Richard, wrote the song he sings in the film, "More Than Wanting You." Walker Edmiston and Elaine DuPont, who play Mark and Jane respectively, wrote "There's a Monster in the Surf."
The film was featured in an episode of Deadly Cinema. The film is listed in Golden Raspberry Award founder John Wilson's book The Official Razzie Movie Guide as one of "The 100 Most Enjoyably Bad Movies Ever Made." It was also featured in an episode of The Twisted Tales of Felix the Cat in which Felix is trapped inside a VCR and has to survive various movies.