A criminal investigation is underway into the circumstances that caused Big Island resident Theresa Butts to be killed in a boating incident on Monday.

The 54-year-old woman, formerly of Alaska, was killed while working aboard the 40-foot passenger vessel Uhane Nui O Naia (Great Spirit of the Dolphin), operated by the tour company Sunlight on Water, based in Kailua-Kona.

Butts’ ex-husband, Dennis, said his former wife worked part-time for Sunlight on Water and was on a manta ray snorkel trip when the incident occurred.

Kona patrol officers responded to the Honokohau Small Boat Harbor shortly after 6 p.m. on Monday following a report of a boating fatality, said Coast Guard Petty Officer Ryan Fisher.

Hawaii County police are working with the Coast Guard and the state Division of Boating and Ocean Recreation to find out what happened, Fisher said. The Coast Guard has jurisdiction in the case.

Dennis Butts told Civil Beat that Theresa died needlessly. He and his daughter Jeanette have spoken to customers and deckhands who were on the boat at the time Theresa died and saw firsthand what happened. He was told by crew members she was hit by the boat’s propellors after she went into the water.

Butts, who worked in the maritime industry in Kodiak and Seward, Alaska for many years, said his family plans to pursue legal action against the tour company.

Phone messages left with Sunlight on Water seeking comment were not returned late Tuesday or Wednesday morning.

Dennis and Theresa Butts formerly owned an industrial welding company that worked on fishing boats. They were featured in the Discovery Channel’s “Alaskan Steel Men” series.