The accident happened at about 2:30 p.m. Wednesday of Greenwich Point, police said.
The other girl who was watertubing with the victim is in Stamford Hospital in stable condition after she suffered tissue wounds from the propeller, Greenwich police Lt. Kraig Gray said.
The two girls who were tubing became entangled with the boat and were struck by the propeller, Gray said.
The accident occurred in an area of Long Island Sound near Great Captains Island, an island a short distance off the Greenwich coastline, he said.
Police have not released the names of the girl who was killed or the other girls involved.
Two other girls in the boat were not injured. The four girls are all students at Greenwich High School, according to Greenwich Time.
The three other teens are 16-years-old as well Gray said.They are all Greenwich residents, he said.
Greenwich police and officials from the Department of Energy and Environmental Protection are investigating the fatal accident, Gray said.
DEEP is the lead investigator because it is responsible for all water-related accidents in the state, he said.
The accident occurred in the waters near Greenwich Point and the Old Greenwich Yacht Club, but the victims are not members of the club, NBC Connecticut said.
Superintendent of Schools William McKersie said the Greenwich Public School system is mourning one of its own.
"This evening, we are mourning the devastating loss of one of our Greenwich High School students, a rising junior, who was involved in a boating accident today on the Long Island Sound. Our thoughts and prayers are with her family at this time of tragedy," he said in a statement issued Wednesday evening. "There are few words that can express the deep compassion we feel for the family of the young girl that has died and for the three other girls involved in the accident. The Greenwich Public School community is ready to support the girls involved and their families in every way possible. Although school is not in session, we will make counselors available for the school communities at the appropriate time."
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