Nine people, including two children, were killed in a mid-air collision between a helicopter and a seaplane near Moscow, said an official.
Rescuers have recovered the bodies of eight of the victims but one person who was reported missing, was still not traced, Tass quoted a representative of the investigation committee Vladimir Markin as saying.
The privately owned Cessna seaplane and a Robinson R44 helicopter collided over the Istrinskoye reservoir late on Saturday and fell into the water, the official said.
The picturesque reservoir, about 60 km from Moscow, is popular for watersports.
"The helicopter and the seaplane have been lifted from the water," he said. "The searchers are trying to find the body of the missing man."
A probe has been ordered into breaches of aviation safety rules, the official said.