José Miranda, the co-founder of Isotope Watches, remembers the first time he ever saw Johanna Nordblad.

It was in the 2016 film “Johanna,” directed by the British filmmaker Ian Derry. The short movie showed the world-ranked free diver swimming, mermaid-like, under the ice on a lake in her native Finland, at times peering up through the clear sheet as if looking through a window.

As a former film producer and water sports enthusiast, Mr. Miranda was “intrigued and compelled after witnessing this remarkable display,” he wrote in an email. “I felt an immediate need to delve deeper into her story and learn more about her extraordinary endeavors.”

His interest has turned into a continuing watch collaboration, with a third Nordblad series planned for release later this year.

When he first reached out in 2017 about teaming up on a diver’s watch, “I saw the kind of passion he has, the love,” Ms. Nordblad recalled in a recent interview. “He said he was inspired, but I was inspired by him, and I could see this was important to him.”

Although not a watch enthusiast, Ms. Nordblad readily agreed to the collaboration, which has yielded two limited-edition series of diver’s timepieces with Swiss movements, both versions of existing models produced by Isotope, whose watches are designed in England and assembled in Switzerland.