The death of a San Juan Island man who went missing at a popular island swimming destination on the evening of Aug. 8 has been determined to be accidental, according to the San Juan County Sheriff’s department.

On Friday, Sheriff Rob Nou said results of an autopsy conducted by the Snohomish County Medical Examiner reveal that Landis Pederson, 20, died of asphyxiation and that the medical examiner ruled his death to be accidental.

Nou said that while death by asphyxiation is consistent with drowning, it’s unclear how a young man who appeared to be in athletic shape would succumb to such a fate.

“We may never really know what happened,” he said. “Sometimes tragic things happen that are hard to explain.”

He said the department may know more about Pederson’s condition at the time of his death after results of toxicology tests are complete, sometime in the next 6-8 weeks.

Pederson, a graduate of Friday Harbor High School, Class of 2009, attended Central Washington University following graduation and returned to San Juan Island late last year to begin working at Friday Harbor House, a local restaurant and inn. He was known for being outgoing, sociable and a skilled conversationalist.

Pederson was swimming with a group of friends at Lawson’s Pond on West Valley Road when he separated himself from the group and then went missing at about 6 p.m.

Equipped with inner tubes, the group launched from a gathering point about midway along the east shore and then paddled to an area near where the pond meets West Valley Road.

At that point, Undersheriff Jon Zerby said Pederson abandoned his inner tube and began swimming back across the middle of the lake, while his friends drifted slowly along the shore.

Zerby said he vanished a short time later and that was the last he was seen.

Noting his clothes and belonging were still at the launch-off point, his friends searched the area for about an hour and tried contacting others with whom he might have left the lake, but  without success. Lacking cell-phone reception, they drove to Friday Harbor to notify authorities that Pederson was missing.

“His body was found a bit too far from where his friends last saw him,” Zerby said. “There aren’t any trees or snags under the water around the area where he was.”

At about 7:45 p.m., deputies, firefighters, EMT’s and members of the Sheriff’s dive team converged at the pond and began searching the lake and surrounding area, but without success.

The following day, with assistance of specially cadaver dogs based in Whatcom County, divers located Pederson’s body about 15 feet below the surface and roughly 175 feet from shore.