NEW YORK >> Ever hear about the gargantuan octopus that dragged a New York City ferry and its 400 passengers to the river bottom nearly 53 years ago?

A cast bronze monument dedicated to the victims of the steam ferry Cornelius G. Kolff recently appeared in Battery Park at the southern tip of Manhattan, erected a stone’s throw from a handful of other somber memorials to soldiers, sailors and mariners lost at sea or on the battlefield.

But if you can’t recall the disaster it could be because the artist behind the memorial, Joseph Reginella, made the whole thing up.

The 250-pound monument, which depicts a Staten Island ferry being dragged down by giant octopus tentacles, is part of a multi-layered hoax that also includes a sophisticated website, a documentary, fabricated newspaper articles and glossy fliers directing tourists to a phantom Staten Island Ferry Disaster Memorial Museum across the harbor.

It took Reginella six months to put it together.

He said the idea for the project came to him while he was taking his 11-year-old nephew from Florida on the ferry between Manhattan and Staten Island.

“He was asking me all kinds of crazy questions like if the waters were shark-infested,” he said. “I said ‘No, but you know what did happen in the ’60s? One of these boats got pulled down by a giant octopus.”

“The story just rolled off the top of my head” and the idea for a mock memorial was born.

It evolved to become “a multimedia art project and social experience — not maliciously — about how gullible people are,” said Reginella, who creates artworks for store windows and amusement parks.

The monument never stays in one spot for more than two days “because the city will come and take it away,” he said, adding that it takes two people to break it down.

“It’s definitely an experience when you see people who don’t know about it. They get this strange look on their face, they stare out at the water and walk away,” he said. “I sit close by with a fishing pole and fish. I eavesdrop on the conversations.”

Sometimes, he said, when he overhears people saying, “How come nobody has ever heard of this?” he’ll interject, offering that the disaster happened on Nov. 22, 1963, a day that the news was dominated by the assassination of President John F. Kennedy.

“It creates a plausibility for them, and they shake their head ‘Maybe.’”

Puzzled tourists looking for the memorial museum on Staten Island and its supposed collection of wreckage with “strange suction-cup-shaped marks” sometimes wonder into the Snug Harbor Cultural Center asking for directions.

The staff at the nearby Staten Island Museum admits it too was puzzled at first.

“We kind of scratched our heads and said we don’t know where it is and started looking further into it, and realized it was a hoax,” said spokeswoman Rachel Somma.

“Most people have the feeling that it’s not a reality. It’s a treasure hunt for them. It’s fun. That’s what we love about it. … It’s great that it gets people out here,” she added.

Melanie Giuliano, who produced a mock documentary for the monument’s website, used her father in the role of a maritime expert and her neighbor as an eyewitness. Reginella’s wife’s co-worker served as the narrator.

“I thought it was an insane idea but I thought it was hilarious,” said the videographer and filmmaker.

One thing about the preposterous story is real. There really was a Cornelius G. Kolff ferry. It ferried passengers for 36 years before becoming a stationary floating dorm for Rikers Island inmates. It was sold for scrap in 2003.