A 53-year-old Massachusetts man has died after he and four other people fell into the West Branch of the Penobscot River during a commercial whitewater rafting excursion.

The Maine Warden Service said Walter Cruz, of Seekonk, Mass., lost consciousness Sunday shortly after he was brought back onto the raft. Officials said Cruz had an apparent medical issue and was pronounced dead at Millinocket Regional Hospital.

The case was referred to the state medical examiner's office for a determination of the cause of death.

Lt. Doug Tibbetts of the Maine Warden Service said Cruz and his 15- and 17-year-old sons were passengers on one of at least seven rafts in the excursion offered by New England Outdoors. The accident occurred shortly before noon below Abol Bridge at Pockwockamus Falls.