"We confirm that so far the bodies of eight dead have been found," AFP cited the deputy governor of the Moscow region as telling the Interfax news agency.
Two of the victims of the crash were children, the emergencies ministry said.
The privately owned Cessna seaplane and a Robinson R44 helicopter collided over the Istrinskoye reservoir late Saturday and fell into the water, the ministry said.
The picturesque reservoir about 60 kilometers (37 miles) from Moscow is popular for watersports.
The emergencies ministry said the helicopter, which was taking a pleasure trip around the area, had three passengers and the pilot on board, while the seaplane had four passengers and the pilot.
Investigators have opened a probe into breaches of aviation safety rules.
A source in the Russian civil aviation agency told RIA Novosti state news agency that the seaplane pilot had not told air traffic control about the flight from an aerodrome beside the reservoir.