The estate of the Pulitzer-winning playwright Paul Zindel has accused the film The Shape of Water of using the late writer’s work without credit, arguing that Guillermo del Toro’s movie, which is leading in Oscar nominations, was “obviously derived” from a 1969 play.

David Zindel, son of the American playwright, told the Guardian he believes his father’s work Let Me Hear You Whisper, a play about a female janitor in a research laboratory who bonds with a captive dolphin and tries to rescue the creature, is a source of inspiration for The Shape of Water. Del Toro’s film was nominated on Tuesday for 13 Oscars, including best picture, best director and best original screenplay.

“We are shocked that a major studio could make a film so obviously derived from my late father’s work without anyone recognizing it and coming to us for the rights,” Zindel, who runs his father’s estate, said in an email to the Guardian.

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The Shape of Water, the critically acclaimed film co-written by Del Toro and Vanessa Taylor, tells the story of a cleaner who works in a Baltimore laboratory in the 1960s and falls in love with a sea creature whom she attempts to rescue. In terms of the broad concept, specific plot points and some characters, the film has close similarities to Let Me Hear You Whisper, which was aired as a TV production nearly 50 years ago.

The creative team behind The Shape of Water, which stars Sally Hawkins, has presented the film as an original idea and has not mentioned Zindel’s work as an inspiration.

A Fox Searchlight spokesperson denied the allegations, which have been circulating on the internet. But this is the first time the playwright’s family has commented on the controversy.

Facebook Twitter Pinterest Scenes from Let Me Hear You Whisper, left, and The Shape of Water. Photograph: YouTube/Allstar/Fox Searchlight Pictures

In both stories, a female cleaner works a night shift at a lab and falls for an aquatic creature that is the subject of mysterious science experiments. Both women develop a relationship by bringing food to the animal and dancing with a mop in front of the tank to the tune of a love song.

The two cleaner characters both learn to communicate with the creatures, and both labs are involved in secretive military operations. The protagonists both discover imminent plans to kill the creature, and both labs mention “vivisection”.

Both women also devise plans to rescue the animal and release it to the sea by sneaking it out in a laundry cart. In Let Me Hear You Whisper, named after a song lyric that the laboratory plays for the dolphin, the creature repeatedly says “hamper” to the protagonist, Helen, to encourage her to get a laundry cart.

Both women are friends with another janitor who helps them – Danielle in one version of Zindel’s work and Zelda in Del Toro’s film, played by Octavia Spencer, who was nominated for an acting Oscar alongside Hawkins.

Facebook Twitter Pinterest Paul Zindel. Photograph: Courtesy David Zindel

There are also major differences in the two stories. In The Shape of Water, the main character, Elisa, is mute and communicates in sign language with the creature.

Helen speaks, but does reference muteness when discussing the dolphin’s inability to talk to the scientists, saying: “Some human beings are mute, you know. Just because they can’t talk, we don’t kill them.”

The Shape of Water also has another significant character: Elisa’s gay friend, played by Richard Jenkins. There are further substantial differences in the endings of the two works.

Paul Zindel, who died in 2003, won the 1971 drama Pulitzer for the play The Effect of Gamma Rays on Man-in-the-Moon Marigolds.

Bonnie Zindel, the playwright’s former wife, said Let Me Hear You Whisper was one of the earliest plays he wrote and one of the first performed on television. The work had a “special place in Paul’s heart”, she said in an email, adding that the playwright was a chemistry teacher before his writing career, which inspired the laboratory setting.

She noted that they watched it together during the Vietnam war and that the themes of the play reflected his belief “that love, not war, is the answer to world peace”.

Fox Searchlight responded in a statement on Thursday, saying: “Guillermo del Toro has never read nor seen Mr Zindel’s play in any form. Mr del Toro has had a 25 year career during which he has made 10 feature films and has always been very open about acknowledging his influences. If the Zindel family has questions about this original work we welcome a conversation with them.”

In a recent interview with Del Toro in a magazine called Written By, the director said the idea originated in part through a conversation with the novelist Daniel Kraus (an associate producer of the film), who suggested a story about a “janitor that kidnaps an amphibian-man from a secret government facility”. Kraus’s website says the film is “based on an original idea” by him and Del Toro. Kraus did not respond to a request for comment.

Viewers of The Shape of Water have increasingly noted the Zindel comparisons on social media in recent months.

“A lot of people are telling us they are struck by the substantial similarities,” David Zindel said in an email. “We are very grateful to Paul Zindel’s fans for bringing this to our attention.”