A 53-year-old Massachusetts man died shortly after a commercial rafting incident Sunday afternoon on the West Branch of the Penobscot River, according to the Maine Warden Service.

Walter Cruz, 53, of Seakonk, Mass., was a passenger on one of at least seven commercial rafts taking a whitewater rafting excursion offered by New England Outdoors when the incident occurred at approximately 11:30 a.m. Sunday, according to Lt. Doug Tibbetts of the Maine Warden Service.

The rafts were below Abol Bridge at Pockwockamu Falls when five people, including Cruz, fell out of the raft they were in. Shortly after Cruz was brought back onto the raft, he lost consciousness for a short period of time, according to Tibbetts.

“When they got Mr. Cruz pulled into the raft, he began to have an apparent medical issue,” Tibbetts said. “He became unconscious momentarily.”

Cruz, who was rafting with his 15- and 17-year-old sons from Coventry, R.I., was transported by ambulance to Millinocket Regional Hospital. He was pronounced dead at 12:41 p.m. at the hospital.

The cause of death is unknown, according to the warden service.

The Maine Medical Examiner’s Office will perform an autopsy Tuesday to determine the cause of death.

The Penobscot River has high, fast water that still is extremely cold, Tibbetts said.