Experienced diver accidentally drowns exploring underwater New Mexico cave

New Mexico authorities confirmed the death of an experienced California diver Thursday after he was helping with the exploration of underwater caves in a well-known swimming hole.

Shane Thompson’s death appears to be an accidental drowning, the initial investigation suggests. The 43-year-old was helping navigate narrow passageways below the Blue Hole in the eastern part of New Mexico, a tourist destination in the community of Santa Rosa.

Santa Rosa Police Chief Jude Gallegos said Thompson was among about 10 people from the ADM Exploration Foundation who were at Blue Hole for a multi-day exploration. The group had been working on surveying the underwater canyon system since 2013.

Thompson and another experienced diver Mike Young dove into Blue Hole on March 26, Gallegos said. They planned to have Young enter the cave and Thompson stay outside in a safety role, but Thompson decided to enter any way, Gallegos said.

“Apparently something went horribly wrong, and he started to panic,” the chief said.

According to The San Diego Tribune, Young told investigators that he and Thompson were looking for passageways when Thompson followed him through a narrow obstruction into a small chamber.

Santa Rosa Police Officer Mike Gauna told the Guadalupe County Communicator that Young started to exit the area, following the safety line. But some silt had been kicked up and it became impossible to see. Thompson pulled on the line extremely hard and it slipped from Young’s hands.

Both dives then became wedged in the passageway. Young swam down to turn around, but Thompson swam upward and took a wrong turn getting trapped in an “unmapped offshoot” in one of the passageways that didn’t lead anywhere, according to the paper.

By the time Young got back to Thompson, he had died.

The state Office of the Medical Investigator said it could be weeks before autopsy results are available.

No more exploration is planned of the underwater cave system at Blue Hole, said Curt Bowen, president of the exploration foundation.

"The cave system below is walled out. That means there is no cave passage left to explore," he said in an email. "We mapped everything we could fit through, and it ended in a tight rock breakdown at a depth of 194 feet."

Thompson was a Navy veteran who started diving at a very young age while growing up in the Florida Keys. After earning his first certification, he went to work for an underwater construction company and later started numerous diving businesses that focused on everything from boat maintenance to salvage work and training.

Last year, Thompson rediscovered the wreckage of the B-36 "Peacemaker" bomber that had crashed in 1952 near Mission Beach. A video posted by Thompson's San Diego-based Advanced Underwater Training business shows his flashlight scanning the engines and other corroded pieces of the plane as he makes his way through the darkness more than 250 feet below the surface.

Family members said Thursday they were struggling with Thompson's death, but they acknowledged that diving was what he loved to do and that he had earned numerous certifications during his lifetime.

The caves have been sealed off since 1976, when two divers in training died after getting separated from their classmates. New Mexico State Police divers quickly found one of the bodies, but it took several weeks to find the other. In the process, police divers made a crude map of some of the unexplored passages.

At that time, one of the divers descended and found himself at the edge of an underwater cliff. His powerful flashlight wasn't enough to see the cave wall across from him or the bottom, sparking only more curiosity.

In 2013, divers with the ADM Exploration Foundation attempted an expedition, but they had little success getting past the tons of rock the city dumped onto the grate to keep people out.

Divers with the foundation returned in 2015 for more excavation work and were able to reach a depth of 160 feet. They returned in late March to continue surveying.

Divers from around the region flock to Blue Hole for fun and certification, as it's one of the best diving spots in the American Southwest. About 8,000 dive permits are sold each year.

The Associated Press contributed to this report.