FRYE ISLAND – The Maine State Police bomb squad Tuesday detonated a World War II-era practice bomb found 10 days ago in Sebago Lake by two Massachusetts divers.

The bomb, which turned out to be a dummy that contained no explosives, had been found in 20-feet-deep water about a mile from the site of two submerged British Corsair airplanes that collided and crashed into the lake in May 1944 during a training exercise.

The five-member bomb team attached an explosive device to the bomb, ran a wire back to the shore and detonated it, said Stephen McCausland, spokesman for the state Department of Public Safety.

“It was a very mild sound that resembled a car backfiring,” McCausland said.

A safety zone measuring roughly three-quarters of a mile was set up around the blast site. Residents of about a half-dozen cottages along the shore were advised to go to the rear of the buildings until the bomb was set off.

Det. Chris Harriman, who viewed the bomb underwater on Sunday, said at the time that he could not tell whether it was live or just a practice device.

“It’s pretty corroded, there’s lots of rust and debris on it,” he said.

Harriman estimated the bomb weighed about 150 pounds.

Frank Federico of Saugus, Mass., and his cousin, John DiFrancesco, found the bomb Aug. 18 while scuba-diving near their summer camp on Frye Island.

“The real mystery is how did it get there,” Federico said.

The two men marked the spot with a weighted dive flag and alerted state police. Federico said he feared passing boats would anchor there and disturb it.

The origin of the bomb is unknown, police said. U.S. and British warplanes often ran training exercises out of Brunswick Naval Air Station and sometimes passed over Sebago Lake.

They would even do gunnery practice over the lake, but did not practice dropping bombs there, they said.

John Garbinski, president of the Maine Aviation Historical Society, said the bomb may have been jettisoned by a plane that needed to get rid of some weight to conserve fuel, or could have been released accidentally.

The bomb was wedged between two rocks, and was still a few inches above the lake bottom, Federico said. The bomb was orange from rust, but not disintegrated, and had no significant markings, he added.