Sea conditions were excellent at midafternoon on a clear day Wednesday off Greenwich, Conn., on Long Island Sound, when a 16-year-old girl was killed and another teenage girl was injured when they were run over by a boat, according to authorities.

The two girls had been riding on a tube towed by a small powerboat and came in contact with its propeller, although investigators have not determined how that occurred, police told the Hartford Courant.

On Thursday, police released the names of those involved; all four were 16 and students at Greenwich High School, and they were friends. Police had yet to make a statement as to whether or not the driver had a boating license.

“I was shocked and scared, because it was four high schoolers. They could be my friends, especially the one passed, it’s just scary,” Matthew Lanagan, a student, told New York TV station WABC.

The Greenwich Time had a photographer at the dock when the boat and girls were brought in, and the newspaper posted 35 photographs of the scene.

In a report by The New York Times, Ian Macmillan, the town’s harbormaster, said it appeared that the two girls fell out of the innertube and into the water before the accident and the propeller struck them when the boat circled back to pick them up.

“This is a shock and a surprise to all of us,” Macmillan said. “It was a beautiful day — perfect conditions. Then out of the blue, something horrific happened.