A state board Friday rejected a plan to destroy the idyllic Cromwell’s swimming cove on Oahu between Diamond Head and Black Point.

The Board of Land and Natural Resources voted 4-2 to deny a permit by the owner of the historic Doris Duke estate to remove a breakwater and fill part of the basin with boulders in an effort to prevent people from injuring themselves by jumping off an inland sea wall into the sandy-bottom basin.

Board members in the majority told the estate’s owner, the nonprofit Doris Duke Foundation for Islamic Art, to try other alternatives short of destroying what some consider a valuable public recreation site and a historic place.

“We ought to try other reasonable alternatives to abate jumping,” said board member Stan Roehrig. “Before we destroy this place, we ought to see if we can fix it.”

The foundation, which operates a museum at the estate, argued that it has tried reasonable measures to prevent jumps that have left two people paraplegic and one quadriplegic. Those efforts include posting signs, erecting a 6-foot fence and hiring security guards.

Konrad Ng, foundation executive director, said dangerous behavior has been on the rise with social media publicizing the cove. He added that a fence put up on the edge of the interior wall in 2014 reduced jumps but that some people now jump from the top of the fence. Also, people are jumping from the breakwater as an alternative.

The foundation proposes dismantling the 140-foot-long rock breakwater and scattering the rocks below the cove’s inner wall so people can’t jump from either structure. A narrower area for swimming would remain and be partially protected by a remnant of a basalt dike upon which much of the breakwater was built.

“This project will maintain public safety while maintaining public access,” Ng told the board.

Several local residents testified Friday against the $2.5 million plan.

“This project is flawed,” said Bill Saunders, a 54-year Black Point resident who said he worked as a gardener for Duke in 1971-72. “It’s just a bad idea.”

Former City Councilman Leigh-Wai Doo applauded the foundation for its effort to improve safety but said its plan would destroy a historic site treasured by residents.

“The question is, What would Doris Duke do?” he said, adding that she helped preserve 83 historic sites around the country. “Would she preserve the site she had the best engineers create? Guaranteed.”

Duke, whose married surname was Cromwell, had the cove built in 1938 as a private yacht basin by dredging a rocky shoreline that previously had been altered to create a saltwater swimming pool. Instead of berthing boats, the basin became coveted for public swimming, snorkeling, shoreline fishing and surf-break access. Even though Duke owned the basin, she allowed public use, as has the foundation.

Fred Fong, a neighbor and physician who swims in the cove, told the board that the fence could be improved, the edge of the inland sea wall could be beveled and the sea wall could be grouted to prevent people from getting onto the wall or fence and jumping.

“Common sense needs to prevail,” he said, calling his suggestions “simple, rational and reasonable.”

Foundation officials said they considered such suggestions as well as others and found them insufficient.

“We did fully consider all alternatives,” said Scott Ezer, a principal with foundation consultant HHF Planners.

Most board members, however, were not convinced.

Voting with Roehrig to deny the project were Keone Downing, Thomas Oi and James Gomes.

Some board members viewed the foundation’s plan as something that would make swimming in what is left of the basin more dangerous because the site, which includes a public shoreline access path and steps leading into the water, would be less protected from ocean swells.

“You folks are going to make it into a dangerous place,” Roehrig said.

Board Chairwoman Suzanne Case expressed support for the plan. Chris Yuen said he would vote against the plan but was recorded as voting the opposite way with Case.

The Office of Conservation and Coastal Lands division of the Department of Land and Natural Resources recommended approving a conservation district use permit for the foundation’s plan.

The foundation, through its attorney, indicated it intends to contest the permit rejection in a quasi-judicial proceeding.