A 39-year-old diver from the Dartmouth area has died while inspecting the dam at Nova Scotia Power's Annapolis Tidal Power Plant on Wednesday.

Annapolis Royal Police Chief Burt McNeil confirmed the man's death several hours after an underwater rescue operation ended.

"My understanding is that he got tangled up and then communication dropped. The standby diver went down and untangled him and brought him up. He was deceased when he got up there," McNeil told CBC News.

"EHS worked on him for a considerable amount of time and probably after about 25 minutes, half hour, declared that he was deceased."

McNeil said the diver was working on the dam's gates. He said he did not know what the diver got tangled on.

An autopsy will be performed Thursday, he said, adding the scene had been turned over to officials with the provincial Department of Labour.

"The scene has been turned over to them, just to make sure, first of all, that his equipment was working properly," he said. McNeil added he suspects it was an accident.

"His helmet has an umbilical cord on it, with the oxygen, that's attached right to him. He would've had oxygen, that I know of. Whether something happened there, I don't know," he said.

Earlier on Wednesday, the utility said the contracted diver was doing an inspection.

"The surface team lost contact with the diver at approximately 1 p.m.," David Rodenhiser, a spokesperson for Nova Scotia Power, said in an email.

The Annapolis Royal Police Department led the rescue effort. The local fire department and two ambulances were also on scene and a LifeFlight helicopter was standing by.

Traffic was stopped for a couple of hours over the causeway between Annapolis Royal and Granville Ferry. The causeway is over the dam. The causeway was reopened as of 3:30 p.m.

"I just heard the fire whistles blowing," said Paul Olshefsky, a bystander. "The rescuers were prepared to be doing something, they were obviously pulling up a stretcher or what appeared to be a stretcher coming up the bank."