CRANE LAKE, Minn. (AP) — Authorities are investigating the death of a scuba diver during a salvage operation on Crane Lake in northern Minnesota.

The 50-year-old man from the town of Embarrass was assisting a group of people Sunday in recovering a piece of sunken machinery from a part of the lake that was about 70 feet (21 meters) deep Sunday when he failed to resurface, the St. Louis County Sheriff’s Office said in a statement. Rescuers found him, but despite lifesaving efforts they were unable to save him.

The salvage operation was based on a barge that was going to be used to transport the sunken equipment back to shore.

The man was trained as a scuba diver but was not affiliated with any recovery or salvage company, the sheriff’s office said.

The accident happened outside the boundary of Voyageurs National Park, which includes part of Crane Lake.