A 53-year-old Seekonk man died Sunday morning during a whitewater rafting trip on Maine’s Penobscot River, according to a spokesman for the Maine Warden Service.

Walter Cruz, of 41 Briarwood Drive, was aboard one of several rafts taking part in a river excursion run by New England Outdoors when the incident occurred Sunday at approximately 11:30 a.m., according to Sgt. Ronald Dunham of the Maine Warden Service in Ashland. The Seekonk man was rafting with his 15- and 17-year-old sons, who are from Coventry.

Cruz was riding in a 15-foot-long commercial raft with seven other people when the raft twisted on its side after flowing over a boulder. Cruz, who Dunham described as a novice rafter, tumbled into the water along with four others.

Cruz swam for a bit as he tried to reach one of the rafts that had proceeded ahead of the toppled craft, witnesses told the warden service. Cruz lost consciousness for a time after making it into a raft.

River guides and at least one excursion member who is a medical professional tried to revive Cruz as the rafting party made its way to a landing below the Pocuwockamu Falls on the West Branch of the Penobscot River, Dunham said. As required by law, New England Outdoors river guides are registered with the state and are trained in CPR and first aid.

Dunham met the rafting group at the landing, he said, helped get Cruz into his vehicle and drove the Seekonk man to a point about six miles from the river where an ambulance could reach the vehicle; all the while wardens performed CPR on Cruz.

Cruz died a short time later, at Millinocket Regional Hospital, Dunham said.

The cause of death is unknown, Dunham said, but the initial indication is that Cruz suffered a heart attack.

“He had some medical issues,” said Dunham.

The divorced Seekonk man apparently had a heart attack previous to Sunday and also had asthma, the warden said.

The Maine medical examiner’s office will perform an autopsy, perhaps as early as today, to determine the cause of death.

Millinocket is about 70 miles north of Bangor, in central Maine. The Penobscot, where the accident occurred, is a popular waterway for outdoor enthusiasts, Dunham noted, and Maine authorities regularly release water from a dam to propel rafts down the river.

The water, particularly at this time of year, is high, fast and cold. The water temperature is about 50 degrees Fahrenheit this week.

Members of the rafting party were wearing wet suits, life jackets and helmets, Dunham said.

“The water is so cold, [wet suits are] pretty much a necessity at this time of year,” he said.

The route down the West Branch is about 8 miles long and rafters generally take about three to four hours to travel the route, sometimes stopping for lunch along the way. Alcohol is not allowed on the trips.

“It’s a day trip type thing,” Dunham said.

Cruz’s party was about two-thirds along the route when the raft he was in came to a boulder around which the river forms a backwash.

“It sometimes tends to trap the [rafts],” he said.

Cruz and the others toppled out of the raft, though no one else was hurt.

An inspection of the rafts showed they were in proper working order with the appropriate safety equipment aboard.

“There was nothing out of the ordinary,” he said. “Everything checked out.”

Dunham met with Cruz’s sons Sunday afternoon at the headquarters of New England Outdoors, where they were taken after the incident, he said.

The boys decided to drive home after they were informed of their father’s death, he said.

—Staff writer Meahgan Wims contributed to this report.

pgrimald@projo.com