The mysterious death of Manhattan swimwear designer Martha Nolan-O’Slatarra at the upscale Montauk Yacht Club is being eyed as a possible accidental overdose, sources said Tuesday.

The 33-year-old Irish beauty was found unconscious at the ritzy club around midnight Aug. 5 aboard a boat named Ripple — one of at least two Grateful Dead-themed crafts owned by insurance mogul Christopher Durnan, sources tell The Post.

An autopsy is pending to determine Nolan-O’Slatarra’s official cause of death — although sources said it was a suspected drug overdose.

Questions have been swirling since the tragic night when Nolan-O’Slatarra was discovered on the Ripple, which was docked at the yacht club. Members reported hearing screams and called 911, before trying to resuscitate the young designer — who was later pronounced dead.

The good Samaritans told The Post they were awakened by a naked man throwing sunscreen at their boat and saw him running down the dock screaming, “Do something!” 

Durnan, 60, a familiar figure at the club, owns the Durnan Group in Rockville Center, which manages the “largest, most successful Workers Compensation Safety Group for Real Estate” according to The Empire State Marine Trades Association, which the group sponsors.

He owns Ripple and a second boat, Hell in a Bucket, which was docked alongside and is also a shout-out to the Grateful Dead, several club members confirmed.

Durnan did not return several requests for comment.

Suffolk County cops have not filed charges or identified any suspects in the case. But authorities have also not publicly ruled out foul play, despite revealing that there was no evidence of violence to the body.

Nolan-O’Slatarra’s death is also being investigated by Suffolk County’s East End Drug Task Force, according to a Tuesday report by Newsday.

“Until you start ruling stuff out, everything is in play,” a source familiar with the investigation told the outlet. 

Nolan-O’Slatarra, a native of the tiny Irish town of Carlow, immigrated to the US, where she started as a bottle service girl in Soho before co-founding East x East, a swimwear label.

“I always knew I wanted to be successful, that I was money-driven, business-driven, and that fashion is a tough industry and it would be a slow road,” she told the Irish Independent last year. 

Her partner in East x East, Dylan Grace, posted a moving tribute on Instagram following her death.

“We dreamed big together, laughed harder than anyone else could understand, and built so much from nothing,” he wrote. “I’m truly blessed and grateful to have had you in my life.”

Nolan-O’Slatarra summered in the Hamptons, where she hosted successful pop-up shows and fashion exhibits for wealthy clientele in Montauk and the surrounding area.

She had finalized her divorce from ex Sam Ryan just months before her death, according to court records reviewed by The Post.

“I represented Mr. Ryan in a matrimonial proceeding. The final papers had been submitted to the court, and before the Judgment of Divorce was issued, I became aware of Ms. Nolan-O’Slatarra’s passing and promptly notified the court,” his attorney,  David Centeno, said in a statement. “Out of respect for the privacy of those involved and my ethical restraints, I cannot discuss whether there was a prenuptial agreement, mediation, or other private arrangements.”

Nolan-O’Slatarra’s heartbroken mother, Elma Nolan, told the Irish Independent on Aug. 7 that her daughter was planning a trip home to Carlow before her death.

“I don’t know what happened to my daughter,” she told the outlet. “I feel numb and in shock.”

Additional reporting by Brandon Cruz, Joe Marino and Peter Senzamici