A longtime Oak Harbor attorney was killed in a diving accident in northern Lake Michigan Monday.

Mark Theune, 58, was pronounced dead at 2:45 p.m. eastern time by a medical examiner in Marquette County. As of Tuesday morning, a cause of death had not yet been determined.

An attorney at the law firm Cohen, Manni, Theune, & Manni for more than 25 years, Theune was the town of Coupeville’s current prosecuting attorney, an active member of his church and an avid diver.

Firm partner Jacob Cohen described Theune as being both an exceptional human being and attorney. Cohen said Theune was kind man who loved his community and the loss will be hard to bear.

“He was loved and respected by everyone in this office,” Cohen said. “He will be deeply missed.”

According to Lt. j.g. Adam Saurin, a spokesman for U.S. Coast Guard Sector Sault Sainte Marie, Theune was diving with Shipwreck Explorers, a charter company out of Manistique in Schoolcraft County when the accident occurred.

The Coast Guard received a mayday call at about noon and a helicopter was dispatched to the vessel’s location, which Saurin said was about five nautical miles northwest of Boulder Reef Rock.

“They stated ‘we have an unconscious diver,’” Saurin said.

Theune, who was an experienced diver, was reportedly diving within a group of nine in waters between 300 and 350 feet in depth, Saurin said. Although it’s not clear what happened, Theune ran into trouble and was brought to the surface.

The dispatched helicopter was about an hour away, and according to Saurin, someone on the vessel performed CPR on Theune for about 45 minutes. A commercial vessel that was nearby also assisted by lending a defibrillator.

Upon the helicopter’s arrival, Theune was hoisted aboard and flown to Marquette General Hospital where he was later pronounced dead. The hospital, which is located off Lake Superior, was selected because it contains a hyperbaric chamber that can treat decompression sickness, commonly referred to as “the bends.”

Cohen said he spoke with Theune’s dive partner and that it’s not yet clear what happened. Any number of things could have gone wrong, from Theune suffering a heart attack to some other unknown problem.

He confirmed that Theune was a diver with more than 35 years of experience. He’s gone diving in locations around the world, from the lakes and quarries of Wisconsin where he grew up to Bikini Atoll in the Pacific Ocean.

Theune was a known underwater photographer and a member of the Maritime Documentation Society’s board. The Puget Sound-based group is dedicated to exploring and documenting existing, undiscovered, and natural historic shipwrecks, according to its website.

Theune was also an accomplished attorney, successfully arguing at least two cases before the Washington State Supreme Court. He gained some fame in 2008 by serving as legal counsel for the Whidbey Animals’ Improvement Foundation during the custody wars for Smiley the dog.

Theune was also a servant in his community, volunteering at St. Augustine Catholic Church in Oak Harbor. He was a member of the church council and was a sacristan — a person in charge of a sacristy and its contents for Mass.

“I can’t tell you what a loss it is,” Cohen said. “It just breaks my heart.”

Theune is survived by his wife, Nancy Theune, an employee with North Whidbey Fire and Rescue. According to Cohen, she has requested that any donations be made to the Southern Poverty Law Center, a nonprofit civil rights organization dedicated to fighting hate and bigotry.

Donations can be mailed to 400 Washington Ave, Montgomery Ala., 36104 or submitted online at www.splcenter.org.